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We use a matched filter to detect compact groups of old, metal-poor stars that we term FOSSILs (Fragments of Old Stellar Systems in Limbo). With size scales on the order of 10 arcminutes, distances ranging from 2 to 200 kpc, and memberships ranging from a handful to several dozen stars, these FOSSILs stand out from the surrounding field and are presumably signatures of, or debris from, ancient star clusters and dwarf galaxies. They may be localized concentrations of stars within more extensive tidal streams, and in some cases may be the signatures of extant but heretofore undetected ultrafaint galaxies. Using magnitudes and colors from the Pan-STARRs survey, we detect ∼70 such FOSSILs at 5σ or greater in a 2200 square degree region in the vicinity of the north Galactic pole. A subsample of more populous FOSSILs that could be candidate ultrafaint dwarf galaxies suggests a total population of 200 such objects within 200 kpc of the Galactic center. Spectroscopic and astrometric follow-up of these FOSSILs will be required to determine the nature of these structures, deepen our understanding of the make-up and accretion history of the Galactic halo, and perhaps alleviate the missing satellites problem.

Deep observations of faint surface brightness stellar tidal streams in external galaxies with LSST are addressed in this White Paper contribution. We propose using the Wide--Fast--Deep survey that contains several nearby galaxies (at distances where the stars themselves are not resolved, i.e., beyond 20 Mpc). In the context of hierarchical galaxy formation, it is necessary to understand the prevalence and properties of tidal substructure around external galaxies based on integrated (i.e., unresolved) diffuse light. This requires collecting observations on much larger samples of galaxies than the Milky Way and M31. We will compare the observed structures to the predictions of cosmological models of galactic halo formation that inform us about the number and properties of streams around Milky Way-like galaxies. The insight gained from these comparisons will allow us to infer the properties of stream progenitors (masses, dynamics, metallicities, stellar populations). The changes in the host galaxies caused by the interactions with the dissolving companion galaxies will be another focus of our studies. We conclude by discussing synergies with WFIRST and Euclid, and also provide concrete suggestions for how the effects of scattered light could be minimized in LSST images to optimize the search for low surface brightness features, such as faint unresolved stellar tidal streams., 13 pages, 2 figures, submitted to Call for White Papers on LSST Cadence Optimization

Although the final observations of the Spitzer Warm Mission are currently scheduled for March 2019, it can continue operations through the end of the decade with no loss of photometric precision. As we will show, there is a strong science case for extending the current Warm Mission to December 2020. Spitzer has already made major impacts in the fields of exoplanets (including microlensing events), characterizing near Earth objects, enhancing our knowledge of nearby stars and brown dwarfs, understanding the properties and structure of our Milky Way galaxy, and deep wide-field extragalactic surveys to study galaxy birth and evolution. By extending Spitzer through 2020, it can continue to make ground-breaking discoveries in those fields, and provide crucial support to the NASA flagship missions JWST and WFIRST, as well as the upcoming TESS mission, and it will complement ground-based observations by LSST and the new large telescopes of the next decade. This scientific program addresses NASA's Science Mission Directive's objectives in astrophysics, which include discovering how the universe works, exploring how it began and evolved, and searching for life on planets around other stars., 75 pages. See page 3 for Table of Contents and page 4 for Executive Summary

We have obtained deep g, r, and i-band Subaru and ultra-deep 3.6 μm IRAC images of parts of the multiply-wrapped stellar stream around the nearby edge-on galaxy NGC 5907. We have fitted the surface brightness measurements of the stream with FSPS stellar population synthesis models to derive the metallicity and age of the brightest parts of the stream. The resulting relatively high metallicity ([Fe/H] = −0.3) is consistent with a major merger scenario but a satellite accretion event cannot be ruled out.

Recent years have seen the discovery of an ever growing number of stellar debris streams and clouds. These structures are typically detected as extended and often curvilinear overdensities of metal-poor stars that stand out from the foreground disk population. The streams typically stretch tens of degrees or more across the sky, even encircling the Galaxy, and range in heliocentric distance from 3 to 100 kpc. This chapter summarizes the techniques used for finding such streams and provides tables giving positions, distances, velocities, and metallicities, where available, for all major streams and clouds that have been detected as of January 2015. Sky maps of the streams are also provided. Properties of individual tidal debris structures are discussed., Comment: 27 pages, 6 figures, Book chapter in Tidal Streams in the Local Group and Beyond, eds. Heidi Newberg and Jeff Carlin

Using the Sloan Digital Sky Survey Data Release 7, we reexamine the Eastern Banded Structure (EBS), a stellar debris stream first discovered in Data Release 5 and more recently detected in velocity space by Schlaufman et al. The visible portion of the stream is 18 degrees long, lying roughly in the Galactic Anticenter direction and extending from Hydra to Cancer. At an estimated distance of 9.7 kpc, the stream is approximately 170 pc across on the sky. The curvature of the stream implies a fairly eccentric box orbit that passes close to both the Galactic center and to the sun, making it dynamically distinct from the nearby Monoceros, Anticenter, and GD-1 streams. Within the stream is a relatively strong, 2 degree-wide concentration of stars with a very similar color-magnitude distribution that we designate Hydra I. Given its prominence within the stream and its unusual morphology, we suggest that Hydra I is the last vestige of the EBS's progenitor, possibly already unbound or in the final throes of tidal dissolution. Though both Hydra I and the EBS have a relatively high velocity dispersion, given the comparatively narrow width of the stream and the high frequency of encounters with the bulge and massive constituents of the disk that such an eccentric orbit would entail, we suggest that the progenitor was likely a globular cluster, and that both it and the stream have undergone significant heating over time., 7 pages, 8 figures, accepted for publication in the Astrophysical Journal

We analyze HST+WFPC2 images of 77 early-type galaxies. Brightness profiles are classed into "core" or "power-law" forms. Cores are typically rounder than power-law galaxies. Nearly all power-laws with central ellipticity >=0.3 have stellar disks, implying that disks are present in power-laws with epsilon, 76 pages, 40 figures, submitted to the Astronomical Journal. The complete postscript version of the paper is available at http://www.noao.edu/noao/staff/lauer/nuker.html (the Nuker Team page)

A low mass, large core radius, and strong tidal tails suggest that the globular cluster Palomar 5 has lost a large fraction of its initial mass over time. If the dynamical evolution of Palomar 5 has been dominated by the effects of mass loss, then the luminosity function should be deficient in low-mass stars. Using deep WFPC2 F555W and F814W photometry, we determine the main sequence luminosity functions both near the cluster center and in a field near the half-light radius. There is no compelling evidence for mass segregation within the cluster, but a comparison of the global mass function of Palomar 5 with those of Omega Cen and M55 indicates an increasing deficiency of stars with progressively lower masses. A fit of the observed luminosity function to theoretical models yields a power-law mass function with an exponent of -0.5. The flatness of the mass function is consistent with models of the dynamical evolution of globular clusters that have lost on the order of 90% of their original stellar mass. We suggest that Palomar 5 has lost a large percentage of its original stellar content as a result of tidal shocking., Comment: 19 LaTeX/AASTeX pages with 8 figures, accepted for publication in the Astronomical Journal

We present deep photometry obtained with the Hubble Space Telescope (HST) in a field in Baade's Window in the Galactic bulge. We derive a luminosity function down to I ~ 24.3, or V ~ 27.5, corresponding to M ~ 0.3 Msun. The luminosity function from the turnoff down to this level appears remarkably similar to that observed in the solar neighborhood. We derive a mass function using both an empirical local mass-luminosity relation and a mass-luminosity relation from recent stellar model calculations, allowing for the presence of binaries and photometric errors. The mass function has a power law form with dN/dM proportional to M^{-2.2} for M >~ 0.7 Msun. However, we find strong evidence for a break in the mass function slope around 0.5-0.7 Msun, with a significantly shallower slope at lower masses. The value of the slope for the low masses depends on the assumed binary fraction and the accuracy of our completeness correction. This mass function should directly reflect the initial mass function., 26 pages, 9 figures, to be published in the Astronomical Journal

We present an F606W-F814W color-magnitude diagram for the Draco dwarf spheroidal galaxy based on Hubble Space Telescope Wide Field Planetary Camera 2 (WFPC2) images. The luminosity function is well sampled to ~3 mag below the turnoff. We see no evidence for multiple turnoffs and conclude that, at least over the field of view of the WFPC2, star formation was primarily single-epoch. If the observed number of blue stragglers is due to extended star formation, then roughly 6% (upper limit) of the stars could be half as old as the bulk of the galaxy. The color difference between the red giant branch and the turnoff is consistent with an old population and is very similar to that observed in the old, metal-poor Galactic globular clusters M68 and M92. Despite its red horizontal branch, Draco appears to be older than M68 and M92 by 1.6 ± 2.5 Gyr, lending support to the argument that the "second parameter" that governs horizontal-branch morphology must be something other than age. Draco's observed luminosity function is very similar to that of M68, and the derived initial mass function is consistent with that of the solar neighborhood.

We discuss recent observational and numerical work on tidal tails in globular clusters. Evidence of tidal tails has now been found in 16 Galactic globulars and 4 globulars in M31. Simulations indicate that mapping of these tidal tails over most of a typical cluster's orbit may be quite feasible. A relatively modest effort in this regard would yield reliable space velocities for those clusters whose tidal tails could be traced to angular separations of a few degrees or more. Mining of forthcoming databases should allow us to trace the individual orbital paths of globular clusters over large portions of the sky. This would enable us to better constrain models of the collapse of the Galaxy and to build up an accurate picture of the distribution of matter in the Galactic halo., Comment: 8 pages, Latex, paspconf.sty; To appear in the Proceedings of the UC Santa Cruz Workshop on Galactic Halos (ed. D. Zaritsky)

The color-magnitude (CM) diagram of the Draco dwarf spheroidal was first studied by Baade & Swope (1961). In addition to finding a general similarity to the CM-diagrams of metal-poor globular clusters, they also detected the anomalous Cepheids and broad giant branch which are characteristic of dwarf spheroidals. The best ground-based CCD CM diagrams of the Draco dwarf spheroidal to date have been presented by Stetson, Vandenberg, & McClure (1985) and Carney & Seitzer (1986, hereafter CS86). Here we describe the first results of an HST program to investigate the stellar population of this galaxy.

We present HST Planetary Camera V and I~band images of the central region of the peculiar giant elliptical galaxy NGC 1316. The inner profile is well fit by a nonisothermal core model with a core radius of 0.41" +/- 0.02" (34 pc). At an assumed distance of 16.9 Mpc, the deprojected luminosity density reaches $\sim 2.0 \times 10^3 L_{\sun}$ pc$^{-3}$. Outside the inner two or three arcseconds, a constant mass-to-light ratio of $\sim 2.2 \pm 0.2$ is found to fit the observed line width measurements. The line width measurements of the center indicate the existence of either a central dark object of mass $2 \times 10^9 M_{\sun}$, an increase in the stellar mass-to-light ratio by at least a factor of two for the inner few arcseconds, or perhaps increasing radial orbit anisotropy towards the center. The mass-to-light ratio run in the center of NGC 1316 resembles that of many other giant ellipticals, some of which are known from other evidence to harbor central massive dark objects (MDO's). We also examine twenty globular clusters associated with NGC 1316 and report their brightnesses, colors, and limits on tidal radii. The brightest cluster has a luminosity of $9.9 \times 10^6 L_{\sun}$ ($M_V = -12.7$), and the faintest detectable cluster has a luminosity of $2.4 \times 10^5 L_{\sun}$ ($M_V = -8.6$). The globular clusters are just barely resolved, but their core radii are too small to be measured. The tidal radii in this region appear to be $\le$ 35 pc. Although this galaxy seems to have undergone a substantial merger in the recent past, young globular clusters are not detected., 21 pages, latex, postscript figures available at ftp://delphi.umd.edu/pub/outgoing/eshaya/fornaxa

We present a new distance estimation for the Milky Way dwarf spheroidal satellite Sculptor obtained from multi-epoch mid-infrared observations of RR Lyrae stars. The 3.6 {\mu}m observations have been acquired with the Infrared Array Camera on board the Spitzer Space Telescope as part of the SMHASH Program. Mid-infrared light curves for 42 RRL were obtained, from which we measured Sculptor's distance modulus to be {\mu} = 19.60 $\pm$ 0.02 (statistical) $\pm$ 0.04 (photometric) mag (with $\sigma_{sys}=$ = 0.09 mag), using the 3.6 {\mu}m empirical period-luminosity relations derived from the Galactic globular cluster M4, or {\mu} = 19.57 $\pm$ 0.02 (statistical) $\pm$ 0.04 (photometric) mag (with $\sigma_{sys}=$ = 0.11 mag) using empirical relations in the same passband recently derived from the Large Magellanic Cloud globular cluster Reticulum. Both these measurements are in good agreement with values presented in previous works with Sculptor RR Lyrae stars in optical bands, and are also consistent with recent near-infrared RR Lyrae results. Best agreement with the literature is found for the latter modulus which is equivalent to a distance of d = 82 $\pm$ 1 (statistical) $\pm$ 2 (photometric) kpc (with $\sigma_{sys}=$ = 4 kpc). Finally, using a subsample of RR Lyrae stars with spectroscopic metallicities, we demonstrate that these distance estimates are not affected by metallicity effects., Comment: 24 pages, 11 figures. Accepted for publication in MNRAS

Stellar tidal streams provide an opportunity to study the motion and structure of the disrupting galaxy as well as the gravitational potential of its host. Streams around the Milky Way are especially promising as phase space positions of individual stars will be measured by ongoing or upcoming surveys. Nevertheless, it remains a challenge to accurately assess distances to stars farther than 10 kpc from the Sun, where we have the poorest knowledge of the Galaxy's mass distribution. To address this we present observations of 32 candidate RR Lyrae stars in the Orphan tidal stream taken as part of the Spitzer Merger History and Shape of the Galactic Halo (SMHASH) program. The extremely tight correlation between the periods, luminosities, and metallicities of RR Lyrae variable stars in the Spitzer IRAC $\mathrm{3.6 \mu m}$ band allows the determination of precise distances to individual stars; the median statistical distance uncertainty to each RR Lyrae star is $2.5\%$. By fitting orbits in an example potential we obtain an upper limit on the mass of the Milky Way interior to 60 kpc of $\mathrm{5.6_{-1.1}^{+1.2}\times 10^{11}\ M_\odot}$, bringing estimates based on the Orphan Stream in line with those using other tracers. The SMHASH data also resolve the stream in line--of--sight depth, allowing a new perspective on the internal structure of the disrupted dwarf galaxy. Comparing with N--body models we find that the progenitor had an initial dark halo mass of approximately $\mathrm{3.2 \times 10^{9}\ M_\odot}$, placing the Orphan Stream's progenitor amongst the classical dwarf spheroidals., Comment: 18 pages, 10 figures. Submitted to MNRAS; comments welcome