index.json

[{"authors":["Carlin, Jeffrey L.","Garling, Christopher T.","Peter, Annika H. G.","Crnojević, Denija","Forbes, Duncan A.","Hargis, Jonathan R.","Mutlu-Pakdil, Burçin","Pucha, Ragadeepika","Romanowsky, Aaron J.","Sand, David J.","Spekkens, Kristine","Strader, Jay","Willman, Beth"],"categories":null,"content":"","date":1573023600,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1573023600,"objectID":"826d321824ebf28f528a5208108ba48c","permalink":"http://jeffcarlin.github.io/publication/ddo44_stream/","publishdate":"2019-11-06T00:00:00-07:00","relpermalink":"/publication/ddo44_stream/","section":"publication","summary":"We report the discovery of a $1$ degree ($\\sim$50 kpc) long stellar tidal stream emanating from the dwarf galaxy DDO 44, a likely satellite of Local Volume galaxy NGC 2403 located $\\sim$70 kpc in projection from its companion. NGC 2403 is a roughly Large Magellanic Cloud stellar-mass galaxy 3 Mpc away, residing at the outer limits of the M 81 group. We are mapping a large region around NGC 2403 as part of our MADCASH (Magellanic Analogs' Dwarf Companions and Stellar Halos) survey, reaching point source depths (90% completeness) of (g, i) = (26.5, 26.2). Density maps of old, metal-poor RGB stars reveal tidal streams extending on two sides of DDO 44, with the streams directed toward NGC 2403. We estimate total luminosities of the original DDO 44 system (dwarf and streams combined) to be $M\\_{i, \\rm{tot}} = −13.4$ and $M\\_{g, \\rm{tot}} = −12.6$, with $\\sim$25−30% of the luminosity in the streams. Analogs of roughly LMC-mass hosts with massive tidally disrupting satellites are rare in the Illustris simulations, especially at large separations such as that of DDO 44. The few analogs that are present in the models suggest that even low-mass hosts can efficiently quench their massive satellites.","tags":[],"title":"Tidal destruction in a low mass galaxy environment: the discovery of tidal tails around DDO 44","type":"publication"},{"authors":[],"categories":[],"content":" In my previous post I discussed our project to find some of the most distant stars in the outskirts of our Milky Way galaxy. (The illustration above shows the fields on the sky that we have observed so far as part of our survey.) In this post, I\u0026rsquo;ll explain more about why we want to find these distant Milky Way halo stars.\nMass of the Milky Way We don\u0026rsquo;t even know the mass of our Galaxy better than about a factor of two. That\u0026rsquo;s like if someone asked me how much I weigh, and I said \u0026ldquo;Oh, somewhere between 125 and 250 pounds.\u0026rdquo; (That\u0026rsquo;s about 57-113 kilograms, for those of you not used to pounds, or about 9-18 stone, if you prefer.) That\u0026rsquo;s a true statement, but not very informative. We live inside the Milky Way, so it\u0026rsquo;s hard to get an idea of the entire Galaxy from our perspective. It\u0026rsquo;s like if you were in downtown Chicago, and you and your friends went to the observation deck of your favorite skyscraper. Do you think that by looking out over the city, you could guess how big it is and how many people live there? Sure, you could each come up with a reasonable guess, but maybe at best within a factor of two (for example, ranging between about 4.5 million to 18 million, or a factor of 2 in either direction from the Chicago metro area\u0026rsquo;s population of roughly 9 million). Seems like a pretty uncertain guess, right? Well, that\u0026rsquo;s how well we know the total mass of our Milky Way galaxy.\n  Various estimates of the mass of the Milky Way. A given study can only estimate the mass that is contained within the distance of the tracers used, so the plot above shows the mass within each radius in the Milky Way. The vertical axis is mass in units of $10^{12}$ (trillions!) of Solar masses (the mass of the Sun, a typical star). You can see that at $R =100$ kpc (kiloparsecs, where 100 kpc is a distance of about 325,000 light years), the estimates for our Galaxy\u0026rsquo;s mass range from less than half a trillion Solar masses to as much as 1.5 trillion. This highlights just how difficult it is to measure our Galaxy\u0026rsquo;s mass. (Image from this recent paper by Eadie \u0026amp; Jurić (2018); their best estimates for the mass are shown as shaded gray regions.)   Fine, but why does it matter whether we know our Galaxy\u0026rsquo;s mass or not? First off, because we live inside of it, the Milky Way is the best-studied galaxy in the Universe. Because of this, we use it as a benchmark to understand other galaxies and the results of computer simulations of galaxy formation and evolution. To know which simulated galaxies to compare to, we need to know how much \u0026ldquo;stuff\u0026rdquo; (gas, stars, and dark matter \u0026ndash; more on that soon) our Galaxy contains.\nAt least half the mass of the Milky Way is in the form of dark matter. What is dark matter? Well, we don\u0026rsquo;t know for sure, but we do know that it\u0026rsquo;s there. It was first definitively shown to exist in the mid-1970s by Vera Rubin, who measured the speed at which stars in the outer parts of nearby galaxies are rotating. The orbit of an object is determined by the amount of mass contained inside its orbit (for example, the Earth\u0026rsquo;s orbit is mostly due to the Sun\u0026rsquo;s gravitational influence, since the Sun makes up most of the mass in the Solar system). But when Rubin compared the rotation speeds she was measuring to what was expected due to the mass we can see (gas, dust, and stars) in the galaxies she studied, she found that all of the galaxies were rotating faster than the visible matter could account for. This means that to account for the galaxies\u0026rsquo; faster rotation, there must be some other mass present that we can\u0026rsquo;t directly see \u0026ndash; this unseen mass is what we call \u0026ldquo;dark matter.\u0026rdquo; It turns out that dark matter makes up the majority of the mass in many (or perhaps most) galaxies. There is a lot of other evidence for the existence of dark matter, and a lot of ongoing study to determine what it is made up of.\nThe reason dark matter is relevant to the discussion at hand is because it makes up most of our Galaxy\u0026rsquo;s mass in the outer regions. Only 1% of the Milky Way\u0026rsquo;s stars are in the halo, with most of them concentrated in the pancake-like disk of our Galaxy. Thus one of the ways to understand our Galaxy\u0026rsquo;s size, mass, and shape is to use the few stars that are present to study its outer parts.\n  Remnants of destroyed dwarf galaxies When large galaxies like the Milky Way form, there are also smaller \u0026ldquo;dwarf galaxies\u0026rdquo; that form with them, and continue to orbit around their larger host galaxy. The image above shows an illustration of the dwarf companions of the Milky Way that were known as of about 10 years ago. We have since found many more. Dwarf galaxies are of particular interest because they have few stars, with the vast majority of their mass made up by dark matter. The number and properties of dwarf galaxies that form around each larger galaxy help us to decide between models of galaxy formation, and in particular between predictions of the properties of dark matter that makes up most of the mass. However, the dwarf galaxies that we see today don\u0026rsquo;t represent all of the dwarfs that the Milky Way has hosted. When these tiny galaxies approach the inner parts of their host galaxy, the stronger gravitational forces they encounter pull them apart. This is illustrated in the video shown below (from Kathryn Johnston and James Bullock), which is a computer simulation of what happens to dwarf galaxies (the colored points) as they orbit in a Milky Way-like galaxy\u0026rsquo;s dark matter halo. You can see that many of them are shredded apart, and their stars become part of an overall \u0026ldquo;halo\u0026rdquo; of stars.\n Shape, density profile of the halo In fact, it is thought that most of the stars in the Milky Way halo came from destroyed dwarf galaxies, and that the outermost portions of the halo are entirely made up of recently ingested dwarf galaxies. This means that by mapping the outer halo, we can infer something about the history of our galaxy. The number and properties of dwarf galaxies that have been swallowed can affect the shape of the halo (for example, if all the dwarf galaxies were concentrated to one side, the halo may look oblong). Also, the number of stars seen in the outer regions may tell us how many dwarfs fell in, and how large they were. In this way we can piece together how many dwarf galaxies were originally hosted by the Milky Way.\nTracers of mass Finally, as mentioned when we discussed dark matter, the motions of stars are determined by the amount of mass inside their orbit. So if we are able to measure the orbits of stars (or even of dwarf galaxies) in the Milky Way, we can use them as \u0026ldquo;tracers\u0026rdquo; to tell us how much mass is contained inside their location in our Galaxy. In the outermost Milky Way, there are very few stars, so in order to really pin down the total mass within, say, 600,000 light years, we need to find as many possible tracers as we can. This is our goal with the RR Lyrae stars \u0026ndash; we want to find them, then measure their motions through space, so that we can use them to determine the mass of our Galaxy. Right now, the only means we have of tracing the Galaxy\u0026rsquo;s mass in the outer parts is dwarf galaxies and star clusters, of which there are very few. This is why we need lots of RR Lyrae stars \u0026ndash; we don\u0026rsquo;t have many tracers in the outer regions, and they\u0026rsquo;re not spread out over the sky. As mentioned in my previous post, we\u0026rsquo;ll eventually find a lot of these variable stars in the outer Milky Way via LSST, but that\u0026rsquo;s no reason not to look for them now! With a group of collaborators, I am doing just that \u0026ndash; the map at the top of this post shows the regions of sky we have searched thus far. It\u0026rsquo;s painstaking work, but slowly we\u0026rsquo;re building up a sample of RR Lyrae variables in the outer Galaxy with which we can probe the mass and history of the build-up of our Galaxy.\n","date":1542224047,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1542224047,"objectID":"70d1ff4f500ee53643237aaba9b45629","permalink":"http://jeffcarlin.github.io/post/dist_rrl_science/","publishdate":"2018-11-14T12:34:07-07:00","relpermalink":"/post/dist_rrl_science/","section":"post","summary":"In my previous post I discussed our project to find some of the most distant stars in the outskirts of our Milky Way galaxy. (The illustration above shows the fields on the sky that we have observed so far as part of our survey.) In this post, I\u0026rsquo;ll explain more about why we want to find these distant Milky Way halo stars.\nMass of the Milky Way We don\u0026rsquo;t even know the mass of our Galaxy better than about a factor of two.","tags":[],"title":"What do we learn by studying the outer Milky Way halo?","type":"post"},{"authors":[],"categories":[],"content":" Hi, folks! In this, the first blog post on my site, I\u0026rsquo;ll explain a bit about one of my research projects that I\u0026rsquo;m especially excited about lately. I\u0026rsquo;ll aim to keep it at a level that is understandable for \u0026ldquo;non-experts,\u0026rdquo; but inevitably there will be some astro jargon that creeps in\u0026hellip; -Jeff\nThe sparsely-populated outermost regions of our Milky Way galaxy are poorly studied. In part, this is because stars of a given type become fainter the more distant they are from us \u0026ndash; think about a flashlight: if I stand a few feet away from you, it will look pretty bright (you could read a book by its light), while if I\u0026rsquo;m a block away, it will just look like a small point of light. This is due to what\u0026rsquo;s often called the \u0026ldquo;inverse square law,\u0026rdquo; which says that light from a given source diminishes in intensity proportional to the square of the distance from the viewer (10 times further away means $10^2$, or 100 times, fainter). This means that the old stars in the most distant parts of the Milky Way\u0026rsquo;s \u0026ldquo;halo\u0026rdquo; are quite faint. Furthermore, it\u0026rsquo;s difficult to estimate the distances to typical stars. So, to study the distant reaches of our Galaxy\u0026rsquo;s stellar halo, we need stars that:\n are intrinsically bright (so we can still detect them even at large distances), are fairly common in old, metal-poor populations such as the Milky Way halo, are easy to pick out from among the other, more numerous, types of stars between us and the outer Galaxy, and whose distances can be easily estimated.    The halo of the Milky Way is the diffuse outer region surrounding the disk, where we live along with most of the gas, dust, and stars in the Galaxy. Although it contains only about 1% of the stars in our Galaxy, the halo gives us vital clues about how the Milky Way has grown and evolved. (Image from Hubblesite.)   RR Lyrae \u0026ndash; pulsating variable Stars For an ongoing project I\u0026rsquo;m working on, the solution we have adopted is to use RR Lyrae stars. These are a type of variable stars named after the first one to be discovered \u0026ndash; the star RR Lyrae. RR Lyrae stars are a type of star whose brightness varies because the entire star is pulsating (growing larger, then shrinking, then growing larger again\u0026hellip;). As the star expands and contracts, its brightness changes in a characteristic way, which can be seen in repeated observations of the star (some examples are seen in the header image above, on the right side). (For history of RR Lyrae, including details of their discovery by Williamina Fleming, see this intro at the AAVSO site.) It turns out that the period of this pulsation (the time it takes to complete one \u0026ldquo;cycle\u0026rdquo; of expansion/contraction) is related to the intrinsic brightness of the star, so once you know the period, you can compare its average measured brightness with the derived intrinsic brightness and determine how far away the RR Lyrae star is.\n  Image of the outer regions of the globular cluster M3. This shows an animation of 4 images of the same field taken over the course of the same night. You can see that most of the stars remain the same as it blinks between the 4 images, but some stars change their brightness with time. Most of these are RR Lyrae variables, which can fairly easily be selected by observing the same field of view multiple times. (Image from this page.)   You can see from the figure above that criterion #3 (\u0026ldquo;are easy to pick out from among the other, more numerous, types of stars\u0026rdquo;) is easily satisfied by revisiting the same field repeatedly and determining which stars change in brightness within a few hours. As we mentioned above, the distances to RR Lyrae stars are easily determined once you establish the period of pulsation (#4 above). RR Lyrae stars are indeed fairly bright, and only occur when stars roughly the mass of the Sun (but with much lower abundances of metals) are in the late stages of their lives. Thus they satisfy all of the criteria we laid out above for ideal tracers of the Milky Way halo.\nNow, RR Lyrae stars are well-studied, and are used frequently to map the inner parts of the Milky Way\u0026rsquo;s halo. However, it has only been recently that it has become feasible to observe these pulsating variables in the outermost halo. This is because it requires a large enough telescope to quickly gather enough light from faint, distant stars, that also has a camera with a large enough field of view that we can map large areas of sky in a reasonable time frame. One example is the Dark Energy Camera (DECam) (built for the Dark Energy Survey) on the 4-meter Blanco telescope at CTIO, which we are using for a survey of the outer halo of the Galaxy.\n  Figures from a paper by Medina et al. (2017) showing first results from our survey. At the right, we show \u0026ldquo;light curves\u0026rdquo; (brightness vs. time within the pulsational period, or \u0026ldquo;phase\u0026rdquo;) of the most distant RR Lyrae from our survey, with template RR Lyrae curves overlaid. The lower left figure shows regions on the sky that we have observed thus far, and the upper left illustrates the distances ($d_{H}$) as a function of position in a small wedge of sky.   The figure above shows results from our first publication about this project. In that paper, we presented a total of 173 RR Lyrae stars in about 120 square degrees of sky, in 40 DECam fields that were observed 20 times each. About 1\u0026frasl;3 of these are in the Sextans dwarf spheroidal galaxy, which happens to be within the field of view, another 2 are in the Leo IV dwarf galaxy, and 3 more are newly-discovered variables in the Leo V dwarf galaxy (see this Medina et al. 2017a paper). Of the remaining RR Lyrae, we found 18 that are beyond 90 kiloparsecs (abbreviated kpc; 90 kpc is about 290,000 light years), including the most distant RR Lyrae yet known around the Milky Way at beyond 200 kpc (650,000 light years; we think the \u0026ldquo;edge\u0026rdquo; of our Galaxy should be around 250-300 kpc \u0026ndash; but that\u0026rsquo;s one of the things we\u0026rsquo;re hoping to find out with this study!). We have now obtained DECam observations of 3 times as many fields, and analysis is ongoing. We hope to expand the sample of RR Lyrae stars at the outer limits of the Milky Way to more than 50 (in about 1% of the sky), so that we can begin to infer global properties of the stellar halo of our Galaxy.\nThis is precursor science in anticipation of (and to develop tools for) the upcoming Large Synoptic Survey Telescope (LSST). LSST will consist of an 8.4-meter optical telescope (currently under construction in Chile), a 3.5-degree diameter field of view, and a 3.2 billion pixel (that\u0026rsquo;s giga-pixel) camera. The planned survey (starting in 2023) will observe roughly half the night sky repeatedly for 10 years, ultimately imaging each patch of sky hundreds of times with each of 6 filters. This deep survey will revolutionize our understanding of time-varying astronomical phenomena (including variable stars, but also supernovae, active galactic nuclei, and many other objects). In fact, LSST will find RR Lyrae to distances more than 3 times further than we are reaching in our current DECam survey, over more than 50 times the sky area. Stay tuned!\nIn my next post I\u0026rsquo;ll explain more about why we want to find these distant Milky Way halo stars.\n","date":1539459247,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1539459247,"objectID":"6333ff9eb1d374287ade7282cf326a6b","permalink":"http://jeffcarlin.github.io/post/dist_rrl/","publishdate":"2018-10-13T12:34:07-07:00","relpermalink":"/post/dist_rrl/","section":"post","summary":"Hi, folks! In this, the first blog post on my site, I\u0026rsquo;ll explain a bit about one of my research projects that I\u0026rsquo;m especially excited about lately. I\u0026rsquo;ll aim to keep it at a level that is understandable for \u0026ldquo;non-experts,\u0026rdquo; but inevitably there will be some astro jargon that creeps in\u0026hellip; -Jeff\nThe sparsely-populated outermost regions of our Milky Way galaxy are poorly studied. In part, this is because stars of a given type become fainter the more distant they are from us \u0026ndash; think about a flashlight: if I stand a few feet away from you, it will look pretty bright (you could read a book by its light), while if I\u0026rsquo;m a block away, it will just look like a small point of light.","tags":[],"title":"Studying the outer Milky Way halo with distant RR Lyrae variable stars","type":"post"},{"authors":["Patel, Ekta","Carlin, Jeffrey L.","Tollerud, Erik J.","Collins, Michelle L. M.","Dooley, Gregory A."],"categories":null,"content":"","date":1538377200,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1538377200,"objectID":"42fe9dba31f33db488d64ede26e32a2f","permalink":"http://jeffcarlin.github.io/publication/patel_m33/","publishdate":"2018-10-01T00:00:00-07:00","relpermalink":"/publication/patel_m33/","section":"publication","summary":"Triangulum (M33) is the most massive satellite galaxy of Andromeda (M31), with a stellar mass of about 3 × 109 M☉. Based on abundance matching techniques, M33's total mass at infall is estimated to be of order 1011 M☉. ΛCDM simulations predict that M33-mass halos host several of their own low-mass satellite companions, yet only one candidate M33 satellite has been detected in deep photometric surveys to date. This `satellites of satellites' hierarchy has recently been explored in the context of the dwarf galaxies discovered around the Milky Way's Magellanic Clouds in the Dark Energy Survey. Here, we discuss the number of satellite galaxies predicted to reside within the virial radius (̃160 kpc) of M33 based on ΛCDM simulations. We also calculate the expected number of satellite detections in N fields of data using various ground-based imagers. Finally, we discuss how these satellite population predictions change as a function of M33's past orbital history. If M33 is on its first infall into M31's halo, its proposed satellites are expected to remain bound to M33 today. However, if M33 experienced a recent tidal interaction with M31, the number of surviving satellites depends strongly on the distance achieved at pericenter due to the effects of tidal stripping. We conclude that a survey extending to ̃100 kpc around M33 would be sufficient to constrain its orbital history and a majority of its satellite population. In the era of WFIRST, surveys of this size will be considered small observing programs.","tags":[],"title":"ΛCDM predictions for the satellite population of M33","type":"publication"},{"authors":["Carlin, Jeffrey L.","Sand, D. J."],"categories":null,"content":"","date":1535785200,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1535785200,"objectID":"7ec921b0a947e2045880e93ff87680b4","permalink":"http://jeffcarlin.github.io/publication/booiii/","publishdate":"2018-09-01T00:00:00-07:00","relpermalink":"/publication/booiii/","section":"publication","summary":"We present proper motion (PM) measurements of Boötes III, an enigmatic stellar satellite of the Milky Way (MW), utilizing data from the second data release of the Gaia mission. By selecting 15 radial velocity confirmed members of Boötes III, along with a likely RR Lyrae member in the vicinity, we measure an error-weighted mean PM of ($\\mu\\_{\\alpha {\\rm cos} \\delta}, \\mu\\_{\\delta} ) = (−1.14, −0.98) \\pm (0.18, 0.20)$ mas/yr. We select and present further stars that may be Boötes III members based on their combined PM and position in the color-magnitude diagram. We caution against assigning membership to stars that are not confirmed spectroscopically, as we demonstrate that there are contaminating stars from the disrupting globular cluster NGC 5466 in the vicinity of the main body of Boötes III, but we note that our results are consistent with previous Boötes III PM estimates that did not include spectroscopic members. Based on the measured PM and other known properties of Boötes III, we derive its Galactocentric velocity and compute its orbit given canonical MW potentials with halo masses of both $0.8 \\times 10^{12} M\\_\\odot$ and $1.6 \\times 10^{12} M\\_\\odot$. These orbits robustly show that Boötes III passed within $\\sim12$ kpc of the Galactic center on an eccentric orbit roughly 140 Myr ago. Additionally, the PM of Boötes III is in excellent agreement with predictions for the retrograde motion of the coincident Styx stellar stream. Given this, along with the small pericenter and metallicity spread of Boötes III itself, we suggest that it is a disrupting dwarf galaxy giving rise to the Styx stellar stream.","tags":[],"title":"Boötes III is a Disrupting Dwarf Galaxy Associated with the Styx Stellar Stream","type":"publication"},{"authors":["Mutlu-Pakdil, Burçin","Sand, David J.","Carlin, Jeffrey L.","Spekkens, Kristine","Caldwell, Nelson","Crnojević, Denija","Hughes, Allison K.","Willman, Beth","Zaritsky, Dennis"],"categories":null,"content":"","date":1533106800,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1533106800,"objectID":"8302b4966898f793a0d637259f20677b","permalink":"http://jeffcarlin.github.io/publication/burcin_ufds/","publishdate":"2018-08-01T00:00:00-07:00","relpermalink":"/publication/burcin_ufds/","section":"publication","summary":"We present deep Magellan/Megacam stellar photometry of four recently discovered faint Milky Way satellites: Sagittarius II (Sgr II), Reticulum II (Ret II), Phoenix II (Phe II), and Tucana III (Tuc III). Our photometry reaches $\\sim2-3$ magnitudes deeper than the discovery data, allowing us to revisit the properties of these new objects (e.g., distance, structural properties, luminosity measurements, and signs of tidal disturbance). The satellite color-magnitude diagrams show that they are all old ($\\sim13.5$ Gyr) and metal poor ([Fe/H] ≲ -2.2). Sgr II is particularly interesting, as it sits in an intermediate position between the loci of dwarf galaxies and globular clusters in the size-luminosity plane. The ensemble of its structural parameters is more consistent with a globular cluster classification, indicating that Sgr II is the most extended globular cluster in its luminosity range. The other three satellites land directly on the locus defined by Milky Way ultra-faint dwarf galaxies of similar luminosity. Ret II is the most elongated nearby dwarf galaxy currently known for its luminosity range. Our structural parameters for Phe II and Tuc III suggest that they are both dwarf galaxies. Tuc III is known to be associated with a stellar stream, which is clearly visible in our matched-filter stellar density map. The other satellites do not show any clear evidence of tidal stripping in the form of extensions or distortions. Finally, we also use archival H I data to place limits on the gas content of each object. ","tags":[],"title":"A Deeper Look at the New Milky Way Satellites: Sagittarius II, Reticulum II, Phoenix II, and Tucana III","type":"publication"},{"authors":["Wang, Haifeng","López-Corredoira, Martín","Carlin, Jeffrey L.","Deng, Licai"],"categories":null,"content":"","date":1530428400,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1530428400,"objectID":"117068bf0b5ca121106d604c28aa4ac9","permalink":"http://jeffcarlin.github.io/publication/haifeng_asymm_motions/","publishdate":"2018-07-01T00:00:00-07:00","relpermalink":"/publication/haifeng_asymm_motions/","section":"publication","summary":"We present a three dimensional velocity analysis of Milky Way disc kinematics using LAMOST K giant stars and the GPS1 proper motion catalogue. We find that Galactic disc stars near the anticentre direction (in the range of Galactocentric distance between R = 8 and 13 kpc and vertical position between Z = -2 and 2 kpc) exhibit asymmetrical motions in the Galactocentric radial, azimuthal, and vertical components. Radial motions are not zero, thus departing from circularity in the orbits; they increase outwards within R ≲ 12 kpc, show some oscillation in the northern (0 ","tags":[],"title":"3D Asymmetrical motions of the Galactic outer disc with LAMOST K giant stars","type":"publication"},{"authors":["Carlin, Jeffrey L.","Sheffield, Allyson A.","Cunha, Katia","Smith, Verne V."],"categories":null,"content":"","date":1525158000,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1525158000,"objectID":"4757d0e1e6a150323af68f10da4683f1","permalink":"http://jeffcarlin.github.io/publication/sgr_hex/","publishdate":"2018-05-01T00:00:00-07:00","relpermalink":"/publication/sgr_hex/","section":"publication","summary":"We analyze chemical abundances of stars in the Sagittarius (Sgr) tidal stream using high-resolution Gemini+GRACES spectra of 42 members of the highest surface-brightness portions of both the trailing and leading arms. Targets were chosen using a 2MASS+WISE color-color selection, combined with the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) radial velocities. In this Letter, we analyze [Fe/H] and $\\alpha$-elements produced by both hydrostatic (O, Mg) and explosive (Si, Ca, Ti) nucleosynthetic processes. The average [Fe/H] for our Sgr stream stars is lower than that for stars in the Sgr core, and stars in the trailing and leading arms show systematic differences in [Fe/H]. Both hydrostatic and explosive elements are depleted relative to Milky Way (MW) disk and halo stars, with a larger gap between the MW trend and Sgr stars for the hydrostatic elements. Chemical abundances of Sgr stream stars show similar patterns to those measured in the core of the Sgr dSph. We explore the ratio of hydrostatic to explosive $\\alpha$-elements $\\left [\\alpha_{\\rm h/ex}\\right ]$ (which we refer to as the _HEx ratio_). Our observed HEx ratio trends for Sgr debris are deficient relative to MW stars. Via simple chemical evolution modeling, we show that these HEx ratio patterns are consistent with a Sgr IMF that lacks the most massive stars. This study provides a link between the chemical properties in the intact Sgr core and the significant portion of the Sgr system's luminosity that is estimated to currently reside in the streams.","tags":[],"title":"Chemical Abundances of Hydrostatic and Explosive Alpha-elements in Sagittarius Stream Stars","type":"publication"},{"authors":["Medina, Gustavo E.","Muñoz, Ricardo R.","Vivas, A. Katherina","Carlin, Jeffrey L.","Förster, Francisco","Martínez, Jorge","Galbany, Lluís","González-Gaitán, Santiago","Hamuy, Mario","de Jaeger, Thomas","Maureira, Juan Carlos","San Martín, Jaime"],"categories":null,"content":"","date":1519887600,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1519887600,"objectID":"50eaec6eeb842d728ee193423966a882","permalink":"http://jeffcarlin.github.io/publication/medina_distant_rrl/","publishdate":"2018-03-01T00:00:00-07:00","relpermalink":"/publication/medina_distant_rrl/","section":"publication","summary":"We report the discovery of distant RR Lyrae stars, including the most distant known in the Milky Way, using data taken in the g-band with the Dark Energy Camera as part of the High cadence Transient Survey (HiTS; 2014 campaign). We detect a total of 173 RR Lyrae stars over a $\\sim120$ deg$^2$ area, including both known RR Lyrae and new detections. The heliocentric distances $d\\_{\\rm H}$ of the full sample range from 9 to $200$ kpc, with 18 of them beyond 90 kpc. We identify three sub-groups of RR Lyrae as members of known systems: the Sextans dwarf spheroidal galaxy, for which we report 46 new discoveries, and the ultra-faint dwarf galaxies Leo IV and Leo V. Following an MCMC methodology, we fit spherical and ellipsoidal profiles of the form $\\rho \\(R\\) \\sim R^n$ to the radial density distribution of RR Lyrae in the Galactic halo. The best fit corresponds to the spherical case, for which we obtain a simple power-law index of $n= -{4.17}_{-0.20}^{+0.18}$, consistent with recent studies made with samples covering shorter distances. The pulsational properties of the outermost RR Lyrae in the sample ($d\\_{\\rm H}  90$ kpc) differ from the ones in the halo population at closer distances. The distribution of the stars in a period-amplitude diagram suggest they belong to Oosterhoff-intermediate or Oosterhoff II groups, similar to what is found in the ultra-faint dwarf satellites around the Milky Way. The new distant stars discovered represent an important addition to the few existing tracers of the Milky Way potential in the outer halo.","tags":[],"title":"Discovery of Distant RR Lyrae Stars in the Milky Way Using DECam","type":"publication"},{"authors":["Xu, Yan","Liu, Chao","Xue, Xiang-Xiang","Newberg, Heidi Jo","Carlin, Jeffrey L.","Xia, Qi-Ran","Deng, Li-Cai","Li, Jing","Zhang, Yong","Hou, Yonghui","Wang, Yuefei","Cao, Zihuang"],"categories":null,"content":"","date":1514790000,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1514790000,"objectID":"6eebacb6f02fdcc606767c5fd03f83fd","permalink":"http://jeffcarlin.github.io/publication/xuyan_lamost_halo/","publishdate":"2018-01-01T00:00:00-07:00","relpermalink":"/publication/xuyan_lamost_halo/","section":"publication","summary":"The radial number density and flattening of the Milky Way's stellar halo is measured with 5351 metal-poor ([Fe/H] ","tags":[],"title":"Mapping the Milky Way with LAMOST - II. The stellar halo","type":"publication"},{"authors":["Carlin, Jeffrey L.","Sand, David J.","Muñoz, Ricardo R.","Spekkens, Kristine","Willman, Beth","Crnojević, Denija","Forbes, Duncan A.","Hargis, Jonathan","Kirby, Evan","Peter, Annika H. G.","Romanowsky, Aaron J.","Strader, Jay"],"categories":null,"content":"","date":1512111600,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1512111600,"objectID":"fb61de99b1f4958f2bb8c798484c4536","permalink":"http://jeffcarlin.github.io/publication/coli_triii/","publishdate":"2017-12-01T00:00:00-07:00","relpermalink":"/publication/coli_triii/","section":"publication","summary":"We present deep, wide-field Subaru Hyper Suprime-Cam photometry of two recently discovered satellites of the Milky Way (MW): Columba I (Col I) and Triangulum II (Tri II). The color-magnitude diagrams of both objects point to exclusively old and metal-poor stellar populations. We re-derive structural parameters and luminosities of these satellites, and find $M\\_{\\rm V, ColI}=-4.2 \\pm 0.2$ for Col I and $M\\_{\\rm V, TriII}=-1.2 \\pm 0.4$ for Tri II, with corresponding half-light radii of ${r}\\_{\\rm h, ColI}=117 \\pm 17$ pc and ${r}\\_{\\rm h, TriII}=21 \\pm 4$ pc. The properties of both systems are consistent with observed scaling relations for MW dwarf galaxies. Based on archival data, we derive upper limits on the neutral gas content of these dwarfs, and find that they lack H I, as do the majority of observed satellites within the MW virial radius. Neither satellite shows evidence of tidal stripping in the form of extensions or distortions in matched-filter stellar density maps or surface-density profiles. However, the smaller Tri II system is relatively metal-rich for its luminosity (compared to other MW satellites), possibly because it has been tidally stripped. Through a suite of orbit simulations, we show that Tri II is approaching pericenter of its eccentric orbit, a stage at which tidal debris is unlikely to be seen. In addition, we find that Tri II may be on its first infall into the MW, which helps explain its unique properties among MW dwarfs. Further evidence that Tri II is likely an ultra-faint dwarf comes from its stellar mass function, which is similar to those of other MW dwarfs.","tags":[],"title":"Deep Subaru Hyper Suprime-Cam Observations of Milky Way Satellites Columba I and Triangulum II","type":"publication"},{"authors":["Pearl, Alan N.","Newberg, Heidi Jo","Carlin, Jeffrey L.","Smith, R. Fiona"],"categories":null,"content":"","date":1509519600,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1509519600,"objectID":"e3e03b44fe0ac8868ca51be67e5246ba","permalink":"http://jeffcarlin.github.io/publication/pearl_local_substruct/","publishdate":"2017-11-01T00:00:00-07:00","relpermalink":"/publication/pearl_local_substruct/","section":"publication","summary":"We confirm, quantify, and provide a table of the coherent velocity substructure of the Milky Way disk within 2 kpc of the Sun toward the Galactic anticenter, with a 0.2 kpc resolution. We use the radial velocities of $\\sim340,000$ F-type stars obtained with the Guoshoujing Telescope (also known as the Large Sky Area Multi-Object Fiber Spectroscopic Telescope, LAMOST), and proper motions derived from the PPMXL catalog. The PPMXL proper motions have been corrected to remove systematic errors by subtracting the average proper motions of galaxies and QSOs that have been confirmed in the LAMOST spectroscopic survey, and that are within $2.5^\\circ$ of the star’s position. We provide the resulting table of systematic offsets derived from the PPMXL proper motion measurements of extragalactic objects identified in the LAMOST spectroscopic survey. Using the corrected phase-space stellar sample, we find statistically significant deviations in the bulk disk velocity of $20$ km s$^{-1}$ or more in the three-dimensional velocities of Galactic disk stars. The bulk velocity varies significantly over length scales of half a kiloparsec or less. The rotation velocity of the disk increases by $20$ km s$^{-1}$ from the Sun’s position to 1.5 kpc outside the solar circle. Disk stars in the second quadrant, within 1 kpc of the Sun, are moving radially toward the Galactic center and vertically toward a point a few tenths of a kiloparsec above the Galactic plane; looking down on the disk, the stars appear to move in a circular streaming motion with a radius of the order of 1 kpc.","tags":[],"title":"A Map of the Local Velocity Substructure in the Milky Way Disk","type":"publication"},{"authors":["Dooley, Gregory A.","Peter, Annika H. G.","Carlin, Jeffrey L.","Frebel, Anna","Bechtol, Keith","Willman, Beth"],"categories":null,"content":"","date":1509519600,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1509519600,"objectID":"2b180aaf3a10bb4f7d671d6c0f6e42fb","permalink":"http://jeffcarlin.github.io/publication/dooley_lmc_missing_sats/","publishdate":"2017-11-01T00:00:00-07:00","relpermalink":"/publication/dooley_lmc_missing_sats/","section":"publication","summary":"Recent discovery of many dwarf satellite galaxies in the direction of the Small and Large Magellanic Clouds (SMC and LMC) provokes questions of their origins, and what they can reveal about galaxy evolution theory. Here, we predict the satellite stellar mass function of Magellanic Cloud-mass host galaxies using abundance matching and reionization models applied to the Caterpillar simulations. Specifically focusing on the volume within 50 kpc of the LMC, we predict a mean of four to eight satellites with stellar mass $M\\_{\\rm star}  10^4 M\\_\\odot$, and three to four satellites with $80 10^5 M\\_\\odot (M\\_{\\rm star}  10^4 M\\_\\odot)$ within the virial volume of each, and 1-3 (1-7) within a single 1.5° diameter field of view, making their discovery likely.","tags":[],"title":"The predicted luminous satellite populations around SMC- and LMC-mass galaxies - a missing satellite problem around the LMC?","type":"publication"},{"authors":["Medina, Gustavo E.","Muñoz, Ricardo R.","Vivas, A. Katherina","Förster, Francisco","Carlin, Jeffrey L.","Martinez, Jorge","Galbany, Lluis","González-Gaitán, Santiago","Hamuy, Mario","de Jaeger, Thomas","Maureira, Juan Carlos","San Martín, Jaime"],"categories":null,"content":"","date":1501570800,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1501570800,"objectID":"d3fa19389c601e7f1c5349dedea711ee","permalink":"http://jeffcarlin.github.io/publication/medina_leov/","publishdate":"2017-08-01T00:00:00-07:00","relpermalink":"/publication/medina_leov/","section":"publication","summary":"During the analysis of RR Lyrae stars (RRLs) discovered in the High Cadence Transient Survey (HiTS) taken with the Dark Energy Camera at the 4 m telescope at Cerro Tololo Inter-American Observatory, we found a group of three very distant, fundamental mode pulsator RR Lyrae (type ab). The location of these stars agrees with them belonging to the Leo V ultra-faint satellite galaxy, for which no variable stars have been reported to date. The heliocentric distance derived for Leo V based on these stars is 173 ± 5 kpc. The pulsational properties (amplitudes and periods) of these stars locate them within the locus of the Oosterhoff II group, similar to most other ultra-faint galaxies with known RRLs. This serendipitous discovery shows that distant RRLs may be used to search for unknown faint stellar systems in the outskirts of the Milky Way.","tags":[],"title":"Serendipitous Discovery of RR Lyrae Stars in the Leo V Ultra-faint Galaxy","type":"publication"},{"authors":["Zhang, Yanqiong","Smith, Martin C.","Carlin, Jeffrey L."],"categories":null,"content":"","date":1477983600,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1477983600,"objectID":"62062a348471325c8d4862ef4393d439","permalink":"http://jeffcarlin.github.io/publication/yanqiong_red_runaways/","publishdate":"2016-11-01T00:00:00-07:00","relpermalink":"/publication/yanqiong_red_runaways/","section":"publication","summary":"Stars ejected from the Galactic Center can be used to place important constraints on the Milky Way potential. Since existing hypervelocity stars are too distant to accurately determine orbits, we have conducted a search for nearby candidates using full three-dimensional velocities. Since the efficacy of such studies is often hampered by deficiencies in proper motion catalogs, we have chosen to utilize the reliable, high-precision Sloan Digital Sky Survey (SDSS) Stripe 82 proper motion catalog. Although we do not find any candidates which have velocities in excess of the escape speed, we identify 226 stars on orbits that are consistent with Galactic Center ejection. This number is significantly larger than what we would expect for halo stars on radial orbits and cannot be explained by disk or bulge contamination. If we restrict ourselves to metal-rich stars, we find 29 candidates with [Fe/H]  -0.8 dex and 10 with [Fe/H]  -0.6 dex. Their metallicities are more consistent with what we expect for bulge ejecta, and so we believe these candidates are especially deserving of further study. We have supplemented this sample using our own radial velocities, developing an algorithm to use proper motions for optimizing candidate selection. This technique provides considerable improvement on the blind spectroscopic sample of SDSS, being able to identify candidates with an efficiency around 20 times better than a blind search.","tags":[],"title":"Red Runaways II: Low-mass Hills Stars in SDSS Stripe 82","type":"publication"},{"authors":["Carlin, Jeffrey L.","Sand, David J.","Price, Paul","Willman, Beth","Karunakaran, Ananthan","Spekkens, Kristine","Bell, Eric F.","Brodie, Jean P.","Crnojević, Denija","Forbes, Duncan A.","Hargis, Jonathan","Kirby, Evan","Lupton, Robert","Peter, Annika H. G.","Romanowsky, Aaron J.","Strader, Jay"],"categories":null,"content":"","date":1472713200,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1472713200,"objectID":"ad6704f41d5298096971716d0e598681","permalink":"http://jeffcarlin.github.io/publication/n2403_dwarf/","publishdate":"2016-09-01T00:00:00-07:00","relpermalink":"/publication/n2403_dwarf/","section":"publication","summary":"We report the discovery of the faintest known dwarf galaxy satellite of a Large Magellanic Cloud (LMC) stellar-mass host beyond the Local Group (LG), based on deep imaging with Subaru/Hyper Suprime-Cam. Magellanic Analog Dwarf Companions And Stellar Halos (MADCASH) J074238+652501-dw lies $\\sim$35 kpc in projection from NGC 2403, a dwarf spiral galaxy at D$\\approx$3.2 Mpc. This new dwarf has $M\\_g=-7.4\\pm0.4$ and a half-light radius of 168$\\pm$70 pc, at the calculated distance of 3.39$\\pm$0.41 Mpc. The color-magnitude diagram reveals no evidence of young stellar populations, suggesting that MADCASH J074238+652501-dw is an old, metal-poor dwarf similar to low-luminosity dwarfs in the LG. The lack of either detected HI gas ($M\\_{\\rm HI} / L\\_{\\rm V} ","tags":[],"title":"First Results from the MADCASH Survey: A Faint Dwarf Galaxy Companion to the Low-mass Spiral Galaxy NGC 2403 at 3.2 Mpc","type":"publication"},{"authors":["Carlin, Jeffrey L.","Liu, Chao","Newberg, Heidi Jo","Beers, Timothy C.","Deng, Licai","Guhathakurta, Puragra","Cao, Zihuang","Hou, Yonghui","Wang, Yuefei","Wu, Yue","Zhang, Yong"],"categories":null,"content":"","date":1462086000,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1462086000,"objectID":"8e07fc11ba7be3e3b6d00e2b3b3f8d17","permalink":"http://jeffcarlin.github.io/publication/shards/","publishdate":"2016-05-01T00:00:00-07:00","relpermalink":"/publication/shards/","section":"publication","summary":"We derive the fraction of substructure in the Galactic halo using a sample of over 10,000 spectroscopically confirmed halo giant stars from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) spectroscopic survey. By observing 100 synthetic models along each line of sight with the LAMOST selection function in that sky area, we statistically characterize the expected halo populations. We define as Stellar Halo Accretion Related Debris Structures (SHARDS) any stars in $\\gt 3\\sigma$ excesses above the model predictions. We find that at least 10% of the Milky Way (MW) halo stars from LAMOST are part of SHARDS. By running our algorithm on smooth halos observed with the LAMOST selection function, we show that the LAMOST data contain excess substructure over all Galactocentric radii $R\\_{\\rm GC} \\lt 40$ kpc, beyond what is expected due to statistical fluctuations and incomplete sampling of a smooth halo. The level of substructure is consistent with the fraction of stars in SHARDS in model halos created entirely from accreted satellites. This work illustrates the potential of vast spectroscopic surveys with high filling factors over large sky areas to recreate the merging history of the MW.","tags":[],"title":"Characterizing the SHARDS of Disrupted Milky Way Satellites with LAMOST","type":"publication"},{"authors":["Newberg, Heidi Jo","Carlin, Jeffrey L."],"categories":null,"content":"","date":1451631600,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1451631600,"objectID":"8da9b087e52a81178941f1d266e319fa","permalink":"http://jeffcarlin.github.io/publication/tidal_streams_volume/","publishdate":"2016-01-01T00:00:00-07:00","relpermalink":"/publication/tidal_streams_volume/","section":"publication","summary":"_From the publisher:_ This volume is written by leading scientists in the field, who review the current state of our knowledge of tidal streams in the Milky Way, the Andromeda galaxy, and in other nearby galaxies.  The cosmological origins of dwarf galaxies and the physical processes by which they are tidally disrupted into streams and incorporated into galaxy halos are discussed. The techniques that have been used to identify tidal streams are presented, and will be useful to researchers who would like to find substructures in the next generation of optical sky surveys, including Pan-STARRS and LSST.  The methods that are currently under development to constrain both large scale distribution of dark matter in the Milky Way and the (small scale) lumpiness of the dark matter distribution are also explained.  The authors also provide motivation for future spectroscopic surveys of Milky Way halo stars, which will aid both in the identification of tidal streams and the constraint of dark matter properties.This volume is aimed at graduate students who are beginning this field of research, but is also a resource for researchers who study tidal streams and related fields.  In addition to presenting the physical processes by which tidal streams are created, it also reviews the current state of the observations and the progress towards utilizing these observations to constrain the distribution of dark matter in the Milky Way. The book will introduce anyone with a background in astrophysics to the field of tidal streams.","tags":[],"title":"Tidal Streams in the Local Group and Beyond","type":"publication"},{"authors":["Carlin, Jeffrey L.","Liu, Chao","Newberg, Heidi Jo","Beers, Timothy C.","Chen, Li","Deng, Licai","Guhathakurta, Puragra","Hou, Jinliang","Hou, Yonghui","Lépine, Sébastien","Li, Guangwei","Luo, A.-Li","Smith, Martin C.","Wu, Yue","Yang, Ming","Yanny, Brian","Zhang, Haotong","Zheng, Zheng"],"categories":null,"content":"","date":1435734000,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1435734000,"objectID":"ec481817798118b046ae2bf5275f011e","permalink":"http://jeffcarlin.github.io/publication/lamost_distances/","publishdate":"2015-07-01T00:00:00-07:00","relpermalink":"/publication/lamost_distances/","section":"publication","summary":"We present a method to estimate distances to stars with spectroscopically derived stellar parameters. The technique is a Bayesian approach with likelihood estimated via comparison of measured parameters to a grid of stellar isochrones, and returns a posterior probability density function for each star’s absolute magnitude. This technique is tailored specifically to data from the Large Sky Area Multi-object Fiber Spectroscopic Telescope (LAMOST) survey. Because LAMOST obtains roughly 3000 stellar spectra simultaneously within each ∼5° diameter “plate” that is observed, we can use the stellar parameters of the observed stars to account for the stellar luminosity function and target selection effects. This removes biasing assumptions about the underlying populations, both due to predictions of the luminosity function from stellar evolution modeling, and from Galactic models of stellar populations along each line of sight. Using calibration data of stars with known distances and stellar parameters, we show that our method recovers distances for most stars within ∼20%, but with some systematic overestimation of distances to halo giants. We apply our code to the LAMOST database, and show that the current precision of LAMOST stellar parameters permits measurements of distances with ∼40% error bars. This precision should improve as the LAMOST data pipelines continue to be refined.","tags":[],"title":"Estimation of Distances to Stars with Stellar Parameters from LAMOST","type":"publication"},{"authors":["Carlin, Jeffrey L.","DeLaunay, James","Newberg, Heidi Jo","Deng, Licai","Gole, Daniel","Grabowski, Kathleen","Jin, Ge","Liu, Chao","Liu, Xiaowei","Luo, A.-Li","Yuan, Haibo","Zhang, Haotong","Zhao, Gang","Zhao, Yongheng"],"categories":null,"content":"","date":1383289200,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1383289200,"objectID":"1edf2548eaf3c836f72dc96a3520736e","permalink":"http://jeffcarlin.github.io/publication/disk_substruct/","publishdate":"2013-11-01T00:00:00-07:00","relpermalink":"/publication/disk_substruct/","section":"publication","summary":"We find that Galactic disk stars near the anticenter exhibit velocity asymmetries in both the Galactocentric radial and vertical components across the midplane as well as azimuthally. These findings are based on Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) spectroscopic velocities for a sample of ~400,000 F-type stars, combined with proper motions from the PPMXL catalog for which we have derived corrections to the zero points based in part on spectroscopically discovered galaxies and QSOs from LAMOST. In the region within 2 kpc outside the Sun's radius and ±2 kpc from the Galactic midplane, we show that stars above the plane exhibit net outward radial motions with downward vertical velocities, while stars below the plane have roughly the opposite behavior. We discuss this in the context of other recent findings, and conclude that we are likely seeing the signature of vertical disturbances to the disk due to an external perturbation.","tags":[],"title":"Substructure in Bulk Velocities of Milky Way Disk Stars","type":"publication"},{"authors":["Carlin, Jeffrey L.","Yam, William","Casetti-Dinescu, Dana I.","Willett, Benjamin A.","Newberg, Heidi J.","Majewski, Steven R.","Girard, Terrence M."],"categories":null,"content":"","date":1342335600,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1342335600,"objectID":"1eb66eff051d8d2e67db8d62bd555a6a","permalink":"http://jeffcarlin.github.io/publication/virgo/","publishdate":"2012-07-15T00:00:00-07:00","relpermalink":"/publication/virgo/","section":"publication","summary":"We present three-dimensional space velocities of stars selected to be consistent with membership in the Virgo stellar substructure. Candidates were selected from SA 103, a single $40' \\times 40'$ field from our proper-motion (PM) survey in Kapteyn's Selected Areas (SAs), based on the PMs, Sloan Digital Sky Survey (SDSS) photometry, and follow-up spectroscopy of 215 stars. The signature of the Virgo substructure is clear in the SDSS color-magnitude diagram (CMD) centered on SA 103, and 16 stars are identified that have high Galactocentric-frame radial velocities ($V\\_{\\rm GSR}  50$ km/s) and lie near the CMD locus of Virgo. The implied distance to the Virgo substructure from the candidates is $14 \\pm 3$ kpc. We derive mean kinematics from these 16 stars, finding a radial velocity $V\\_{\\rm GSR} = 153 \\pm 22$ km/s and proper motions $(\\mu\\_{\\alpha {\\rm cos} \\delta}, \\mu\\_\\delta) = (- 5.24, -0.91) \\pm (0.43, 0.46)$ mas/yr. From the mean kinematics of these members, we determine that the Virgo progenitor was on an eccentric ($e \\sim 0.8$) orbit that recently passed near the Galactic center (pericentric distance $R\\_{\\rm p} \\sim 6$ kpc). This destructive orbit is consistent with the idea that the substructure(s) in Virgo originated in the tidal disruption of a Milky Way satellite. N-body simulations suggest that the entire cloud-like Virgo substructure (encompassing the Virgo Overdensity and the Virgo Stellar Stream) is likely the tidal debris remnant from a recently disrupted massive ($\\sim 10^9 M\\_\\odot$) dwarf galaxy. The model also suggests that some other known stellar overdensities in the Milky Way halo (e.g., the Pisces Overdensity and debris near NGC 2419 and SEGUE 1) are explained by the disruption of the Virgo progenitor.","tags":[],"title":"The Origin of the Virgo Stellar Substructure","type":"publication"},{"authors":["Carlin, Jeffrey L.","Lépine, Sébastien","Newberg, Heidi Jo","Deng, Li-Cai","Beers, Timothy C.","Chen, Yu-Qin","Christlieb, Norbert","Fu, Xiao-Ting","Gao, Shuang","Grillmair, Carl J.","Guhathakurta, Puragra","Han, Zhan-Wen","Hou, Jin-Liang","Lee, Hsu-Tai","Li, Jing","Liu, Chao","Liu, Xiao-Wei","Pan, Kai-Ke","Sellwood, J. A.","Wang, Hong-Chi","Yang, Fan","Yanny, Brian","Zhang, Yue-Yang","Zheng, Zheng","Zhu, Zi"],"categories":null,"content":"","date":1341126000,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1341126000,"objectID":"830815848d39102e0fabdf9fe889c2f2","permalink":"http://jeffcarlin.github.io/publication/lamost_targeting/","publishdate":"2012-07-01T00:00:00-07:00","relpermalink":"/publication/lamost_targeting/","section":"publication","summary":"We describe a general target selection algorithm that is applicable to any survey in which the number of available candidates is much larger than the number of objects to be observed. This routine aims to achieve a balance between a smoothly-varying, well-understood selection function and the desire to preferentially select certain types of targets. Some target-selection examples are shown that illustrate different possibilities of emphasis functions. Although it is generally applicable, the algorithm was developed specifically for the LAMOST Experiment for Galactic Understanding and Exploration (LEGUE) survey that will be carried out using the Chinese Guo Shou Jing Telescope. In particular, this algorithm was designed for the portion of LEGUE targeting the Galactic halo, in which we attempt to balance a variety of science goals that require stars at fainter magnitudes than can be completely sampled by LAMOST. This algorithm has been implemented for the halo portion of the LAMOST pilot survey, which began in October 2011.","tags":[],"title":"An algorithm for preferential selection of spectroscopic targets in LEGUE","type":"publication"},{"authors":["Carlin, Jeffrey L.","Majewski, Steven R.","Casetti-Dinescu, Dana I.","Law, David R.","Girard, Terrence M.","Patterson, Richard J."],"categories":null,"content":"","date":1326610800,"expirydate":-62135596800,"kind":"page","lang":"en","lastmod":1326610800,"objectID":"f196c6978d3c4c6d8c95d5e3074f5c80","permalink":"http://jeffcarlin.github.io/publication/sgr_stream_sas/","publishdate":"2012-01-15T00:00:00-07:00","relpermalink":"/publication/sgr_stream_sas/","section":"publication","summary":"We present three-dimensional (3D) kinematics of Sagittarius (Sgr) trailing tidal debris in six fields located 70°-130° along the stream from the Sgr dwarf galaxy core. The data are from our proper-motion (PM) survey of Kapteyn's Selected Areas, in which we have measured accurate PMs to faint magnitudes in ~40' × 40' fields evenly spaced across the sky. The radial velocity (RV) signature of Sgr has been identified among our follow-up spectroscopic data in four of the six fields and combined with mean PMs of spectroscopically confirmed members to derive space motions of Sgr debris based on ~15-64 confirmed stream members per field. These kinematics are compared to predictions of the Law \u0026 Majewski model of Sgr disruption; we find reasonable agreement with model predictions in RVs and PMs along Galactic latitude. However, an upward adjustment of the local standard of rest velocity (ΘLSR) from its standard 220 km/s to at least 232 ± 14 km/s (and possibly as high as 264 ± 23 km/s) is necessary to bring 3D model debris kinematics and our measurements into agreement. Satisfactory model fits that simultaneously reproduce known position, distance, and RV trends of the Sgr tidal streams, while significantly increasing Θ$\\_{\\rm LSR}$, could only be achieved by increasing the Galactic bulge and disk mass while leaving the dark matter halo fixed to the best-fit values from Law \u0026 Majewski. We derive low-resolution spectroscopic abundances along this stretch of the Sgr stream and find a constant [Fe/H] ~ -1.15 (with ~0.5 dex scatter in each field—typical for dwarf galaxy populations) among the four fields with reliable measurements. A constant metallicity suggests that debris along the ~60° span of this study was all stripped from Sgr on the same orbital passage.","tags":[],"title":"Kinematics and Chemistry of Stars along the Sagittarius Trailing Tidal Tail and Constraints on the Milky Way Mass Distribution","type":"publication"}]