Lee R. Spitler

UV LUMINOSITY FUNCTIONS AT REDSHIFTS z ∼ 4 TO z ∼ 10: 10,000 GALAXIES FROM HST LEGACY FIELDS* **

The remarkable Hubble Space Telescope?(HST) data sets from the CANDELS, HUDF09, HUDF12, ERS, and BoRG/HIPPIES programs have allowed us to map the evolution of the rest-frame UV luminosity function (LF) from to . We develop new color criteria that more optimally utilize the full wavelength coverage from the optical, near-IR, and mid-IR observations over our search fields, while simultaneously minimizing the incompleteness and eliminating redshift gaps. We have identified 5859, 3001, 857, 481, 217, and 6 galaxy candidates at , , , , , and , respectively, from the ?1000 arcmin2 area covered by these data sets. This sample of >10,000 galaxy candidates at is by far the largest assembled to date with HST. The selection of 4?8 candidates over the five CANDELS fields allows us to assess the cosmic variance; the largest variations are at . Our new LF determinations at and span a 6 mag baseline and reach to ?16 AB mag. These determinations agree well with previous estimates, but the larger samples and volumes probed here result in a more reliable sampling of galaxies and allow us to reassess the form of the UV LFs. Our new LF results strengthen our earlier findings to significance for a steeper faint-end slope of the UV LF at , with ? evolving from at to at (and at ), consistent with that expected from the evolution of the halo mass function. We find less evolution in the characteristic magnitude M* from to the observed evolution in the LF is now largely represented by changes in . No evidence for a non-Schechter-like form to the z ? 4?8 LFs is found. A simple conditional LF model based on halo growth and evolution in the M/L ratio of halos provides a good representation of the observed evolution.

Galaxy stellar mass functions from ZFOURGE/CANDELS: an excess of low-mass galaxies since z=2 and the rapid buildup of quiescent galaxies

Using observations from the FourStar Galaxy Evolution Survey (ZFOURGE), we obtain the deepest measurements to date of the galaxy stellar mass function (SMF) at 0.2 < z < 3. ZFOURGE provides well-constrained photometric redshifts made possible through deep medium-bandwidth imaging at 1-2 μm. We combine this with Hubble Space Telescope imaging from the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey, allowing for the efficient selection of both blue and red galaxies down to stellar masses of ~109.5 M ☉ at z ~ 2.5. The total surveyed area is 316 arcmin2 distributed over three independent fields. We supplement these data with the wider and shallower NEWFIRM Medium-Band Survey to provide stronger constraints at high masses. Several studies at z ≤ 1.5 have revealed a steepening of the slope at the low-mass end of the SMF, leading to an upturn at masses <1010 M ☉ that is not well described by a standard single-Schechter function. We find evidence that this feature extends to at least z ~ 2 and that it can be found in both the star-forming and quiescent populations individually. The characteristic mass (M*) and slope at the lowest masses (α) of a double-Schechter function fit to the SMF stay roughly constant at Log(M/M ☉) ~ 10.65 and ~ – 1.5, respectively. The SMF of star-forming galaxies has evolved primarily in normalization, while the change in shape is relatively minor. Our data allow us, for the first time, to observe a rapid buildup at the low-mass end of the quiescent SMF. Since z = 2.5, the total stellar mass density of quiescent galaxies (down to 109 M ☉) has increased by a factor of ~12, whereas the mass density of star-forming galaxies only increases by a factor of ~2.2.

The most luminous z ∼ 9-10 galaxy candidates yet found: The luminosity function, cosmic star-formation rate, and the first mass density estimate at 500 Myr

We present the discovery of four surprisingly bright (H160 � 26 27 mag AB) galaxy candidates at z � 9 10 in the complete HST CANDELS WFC3/IR GOODS-N imaging data, doubling the number of z � 10 galaxy candidates that are known, just �500 Myr after the Big Bang. Two similarly bright sources are also detected in a systematic re-analysis of the GOODS-S data set. Three of the four galaxies in GOODS-N are significantly detected at 4.5 6.2� in the very deep Spitzer/IRAC 4.5µm data, as is one of the GOODS-S candidates. Furthermore, the brightest of our candidates (at z = 10.2 ± 0.4) is robustly detected also at 3.6µm (6.9�), revealing a flat UV spectral energy distribution with a slope � = 2.0±0.2, consistent with demonstrated trends with luminosity at high redshift. The abundance of such luminous candidates suggests that the luminosity function evolves more significantly in �∗ than in L∗ at z & 8 with a higher number density of bright sources than previously expected. Despite the discovery of these luminous candidates, the cosmic star formation rate density for galaxies with SFR > 0.7 M⊙ yr −1 shows an order-of-magnitude increase in only 170 Myr from z � 10 to z � 8, consistent with previous results given the dominance of low-luminosity sources to the total SFR density. Based on the IRAC detections, we derive galaxy stellar masses at z � 10, finding that these luminous objects are typically 10 9 M⊙. This allows for a first estimate of the cosmic stellar mass density at z � 10 resulting in log10 �∗ = 4.7 +0.5 −0.8 M⊙ Mpc −3 for galaxies brighter than MUV � 18. The remarkable brightness, and hence luminosity, of these z � 9 10 candidates highlights the opportunity for deep spectroscopy to determine their redshift and nature, demonstrates the value of additional search fields covering a wider area to understand star-formation in the very early universe, and highlights the opportunities for JWST to map the buildup of galaxies at redshifts much earlier than z � 10. Subject headings: galaxies: evolution — galaxies: high-redshift — galaxies: luminosity function

Quantifying the coexistence of massive black holes and dense nuclear star clusters

In large spheroidal stellar systems, such as elliptical galaxies, one invariably finds a 10 6 -10 9 M ⊙ supermassive black hole at their centre. In contrast, within dwarf elliptical galaxies one predominantly observes a 10 5_ 10 7 M ⊙ nuclear star cluster. To date, few galaxies have been found with both types of nuclei coexisting and even less have had the masses determined for both central components. Here, we identify one dozen galaxies housing nuclear star clusters and supermassive black holes whose masses have been measured. This doubles the known number of such hermaphrodite nuclei - which are expected to be fruitful sources of gravitational radiation. Over the host spheroid (stellar) mass range 10 8_ 10 11 M ⊙ , we find that a galaxys nucleus-to-spheroid (baryon) mass ratio is not a constant value but decreases from a few per cent to ~0.3 per cent such that log[(M BH + M NC )/M sph ] = -(0.39 ± 0.07) Iog[M sph /10 10 M ⊙ ] ― (2.18 ± 0.07). Once dry merging commences and the nuclear star clusters disappear, this ratio is expected to become a constant value. As a byproduct of our investigation, we have found that the projected flux from resolved nuclear star clusters is well approximated with Sersic functions having a range of indices from ~0.5 to ~3, the latter index describing the Milky Ways nuclear star cluster.

Globular clusters in Virgo ellipticals: Unexpected results for giants and dwarfs from Advanced Camera for Surveys imaging

We have analyzed archival Hubble Space Telescope Advanced Camera for Surveys images in g and z of the globular cluster (GC) systems of 53 ellipticals in the Virgo Cluster, spanning massive galaxies to dwarf ellipticals (dEs). Several new results emerged. (1) In the giant ellipticals (gEs) M87 and NGC 4649, there is a correlation between luminosity and color for individual blue (metal-poor) GCs, such that more massive GCs are more red (metal-rich). A plausible interpretation of this result is self-enrichment, and a speculative suggestion is that these GCs once possessed dark matter halos. (2) The dispersion in color is nearly twice as large for the metal-rich GCs as for the metal-poor GCs. However, there is evidence for a nonlinear relation between g - z and metallicity, and the dispersion in metallicity may be the same for both subpopulations. (3) Very luminous, intermediate-color GCs are common in gEs. These objects may be remnants of many stripped dwarfs, analogs of ω Cen in the Galaxy. (4) There is a continuity of GC system colors from gEs to some dEs; in particular, many dEs have metal-rich GC subpopulations. We also confirm the GC color-galaxy luminosity relations found previously for both metal-poor and metal-rich GC subpopulations. (5) There are large differences in GC specific frequency among dEs, independent of the presence of a nucleus and the fraction of metal-rich GCs. Over -15 < MB < -18 we find little correlation between specific frequency and MB. But we do find evidence for two separate SN classes of dEs: those with B-band SN ~ 2 and those with populous GC systems that have SN ranging from ~5 to 20 with median SN ~ 10. Together, these points suggest multiple formation channels for dEs in the Virgo Cluster. (6) The peak of the GC luminosity function (GCLF) is the same for both gEs and dEs. This is contrary to expectations of dynamical friction on massive GCs, unless the primordial GCLF varies between gEs and dEs. Among gEs the GCLF turnover varies by a surprisingly small 0.05 mag, an encouraging result for its use as an accurate standard candle.

The SLUGGS Survey : kinematics for over 2500 globular clusters in 12 early-type galaxies

We present a spectro-photometric survey of 2522 extragalactic globular clusters (GCs) around twelve early-type galaxies, nine of which have not been published previously. Combining space‐based and multi‐colour wide field ground‐based imagi ng, with spectra from the Keck DEIMOS instrument, we obtain an average of 160 GC radial velocities per galaxy, with a high velocity precision of � 15 km s 1 per GC. After studying the photometric properties of the GC systems, such as their spatial and colour distribut ions, we focus on the kinematics of metal-poor (blue) and metal-rich (red) GC subpopulations to an average distance of � 8 effective radii from the galaxy centre. Our results show that for some systems the bimodality in GC colour is also present in GC kinematics. The kinematics of the red GC subpopulations are strongly coupled with the host galaxy stellar kinematics. The blue GC subpopulations are more dominated by random motions, especially in the outer regions, and decoupled fro m the red GCs. Peculiar GC kinematic profiles are seen in some galaxies: the blue GCs in NGC 821 rotate along the galaxy minor axis, whereas the GC system of the lenticular galaxy NGC 7457 appears to be strongly rotation supported in the outer region. We supplement our galaxy sample with data from the literature and carry out a number of tests to study the kinematic differences between the two GC subpopulations. We confirm that the GC kinematics are coupled with the host galaxy properties and find that the velocity kurtosis and the slope of their velocity dispersion profiles is different between the two GC subpopulations in more massive galaxies.

The SAGES Legacy Unifying Globulars and GalaxieS Survey (SLUGGS): Sample definition, methods, and initial results

We introduce and provide the scientific motivation for a wide-field photometric and spectroscopic chemodynamical survey of nearby early-type galaxies (ETGs) and their globular cluster (GC) systems. The SAGES Legacy Unifying Globulars and GalaxieS (SLUGGS) survey is being carried out primarily with Subaru/Suprime-Cam and Keck/DEIMOS. The former provides deep gri imaging over a 900 arcmin2 field-of-view to characterize GC and host galaxy colors and spatial distributions, and to identify spectroscopic targets. The NIR Ca II triplet provides GC line-of-sight velocities and metallicities out to typically ~8 R e, and to ~15 R e in some cases. New techniques to extract integrated stellar kinematics and metallicities to large radii (~2-3 R e) are used in concert with GC data to create two-dimensional (2D) velocity and metallicity maps for comparison with simulations of galaxy formation. The advantages of SLUGGS compared with other, complementary, 2D-chemodynamical surveys are its superior velocity resolution, radial extent, and multiple halo tracers. We describe the sample of 25 nearby ETGs, the selection criteria for galaxies and GCs, the observing strategies, the data reduction techniques, and modeling methods. The survey observations are nearly complete and more than 30 papers have so far been published using SLUGGS data. Here we summarize some initial results, including signatures of two-phase galaxy assembly, evidence for GC metallicity bimodality, and a novel framework for the formation of extended star clusters and ultracompact dwarfs. An integrated overview of current chemodynamical constraints on GC systems points to separate, in situ formation modes at high redshifts for metal-poor and metal-rich GCs.

Transformation of a Star into a Planet in a Millisecond Pulsar Binary

Timing observations of a millisecond pulsar reveal a planet that is far denser than any known planet. Millisecond pulsars are thought to be neutron stars that have been spun-up by accretion of matter from a binary companion. Although most are in binary systems, some 30% are solitary, and their origin is therefore mysterious. PSR J1719−1438, a 5.7-millisecond pulsar, was detected in a recent survey with the Parkes 64-meter radio telescope. We show that this pulsar is in a binary system with an orbital period of 2.2 hours. The mass of its companion is near that of Jupiter, but its minimum density of 23 grams per cubic centimeter suggests that it may be an ultralow-mass carbon white dwarf. This system may thus have once been an ultracompact low-mass x-ray binary, where the companion narrowly avoided complete destruction.

Uniting old stellar systems: from globular clusters to giant ellipticals

Elliptical galaxies and globular clusters (GCs) have traditionally been regarded as physically distinct entities due to their discontinuous distribution in key scaling diagrams involving size, luminosity and velocity dispersion. Recently this distinctness has been challenged by the discovery of stellar systems with mass intermediate between those of GCs and dwarf ellipticals (such as ultracompact dwarfs and dwarf galaxy transition objects). Here we examine the relationship between the virial and stellar mass for a range of old stellar systems, from GCs to giant ellipticals, and including such intermediate-mass objects (IMOs). Improvements on previous work in this area include the use of (i) near-infrared magnitudes from the Two Micron All Sky Survey (2MASS), (ii) aperture corrections to velocity dispersions, (iii) homogeneous half-light radii and (iv) accounting for the effects of non-homology in galaxies. We find a virial-to-stellar mass relation that ranges from ∼10 4 M ⊙ systems (GCs) to ∼10 12 M⊙ systems (elliptical galaxies). The lack of measured velocity dispersions for dwarf ellipticals with - 16 > M K > - 18 (∼ 10 8 M ⊙ ) currently inhibits our ability to determine how, or indeed if, these galaxies connect continuously with GCs in terms of their virial-to-stellar mass ratios. We find elliptical galaxies to have roughly equal fractions of dark and stellar matter within a virial radius; only in the most massive (greater than 10 12 M ⊙ ) ellipticals does dark matter dominate the virial mass. Although the IMOs reveal slightly higher virial-to-stellar mass ratios than lower mass GCs, this may simply reflect our limited understanding of their initial mass function (and hence their stellar mass-to-light ratios) or structural properties. We argue that most of these IMOs have similar properties to massive GCs, i.e. IMOs are essentially massive star clusters. Only the dwarf spheroidal galaxies exhibit behaviour notably distinct from the other stellar systems examined here, i.e. they display a strongly increasing virial-to-stellar mass ratio (equivalent to higher dark matter fractions) with decreasing stellar mass. The data used in this study are available in electronic format.

The SFR-M* Relation and Empirical Star-Formation Histories from ZFOURGE at 0.5 < z < 4

We explore star-formation histories (SFHs) of galaxies based on the evolution of the star-formation rate stellar mass relation (SFR-M*). Using data from the FourStar Galaxy Evolution Survey (ZFOURGE) in combination with far-IR imaging from the Spitzer and Herschel observatories we measure the SFR-M* relation at 0.5 < z < 4. Similar to recent works we find that the average infrared SEDs of galaxies are roughly consistent with a single infrared template across a broad range of redshifts and stellar masses, with evidence for only weak deviations. We find that the SFR-M* relation is not consistent with a single power-law of the form SFR ~ M*^a at any redshift; it has a power-law slope of a~1 at low masses, and becomes shallower above a turnover mass (M_0) that ranges from 10^9.5 - 10^10.8 Msol, with evidence that M_0 increases with redshift. We compare our measurements to results from state-of-the-art cosmological simulations, and find general agreement in the slope of the SFR-M* relation albeit with systematic offsets. We use the evolving SFR-M* sequence to generate SFHs, finding that typical SFRs of individual galaxies rise at early times and decline after reaching a peak. This peak occurs earlier for more massive galaxies. We integrate these SFHs to generate mass-growth histories and compare to the implied mass-growth from the evolution of the stellar mass function. We find that these two estimates are in broad qualitative agreement, but that there is room for improvement at a more detailed level. At early times the SFHs suggest mass-growth rates that are as much as 10x higher than inferred from the stellar mass function. However, at later times the SFHs under-predict the inferred evolution, as is expected in the case of additional growth due to mergers.