50 research outputs found
The Relation between Dynamical Mass-to-light Ratio and Color for Massive Quiescent Galaxies out to z ~ 2 and Comparison with Stellar Population Synthesis Models
Article / Letter to editorSterrewach
Steeper, Flatter, or Just "Salpeter"? Evidence from Galaxy Evolution and Galaxy Clusters
A single-slope "Salpeter" IMF overpredicts the stellar M/L ratio of local
elliptical galaxies by about a factor of 2, which requires the IMF to be
flatter below about one solar mass. On the other hand a Salpeter IMF for stars
more massive than the sun predicts an evolution with redshift of the
fundamental plane of ellipticals in clusters which is in agreement with the
observations and a formation at z>~3 for these galaxies. A "Salpeter" IMF for
1<M<40 solar masses also predicts the observed amount of heavy elements (oxygen
and silicon) in clusters of galaxies.Comment: 10 pages, 7 figures, to appear on "IMF@50: The Initial Mass Function
50 Years Later", ed. E. Corbelli, F. Palla, & H. Zinnecker (Dordrecht:
Kluwer), in press. Invited talk at the International Workshop held in Abbazia
di Spineto, Tuscany, Italy -- May 16-20, 200
The outer halos of elliptical galaxies
Recent progress is summarized on the determination of the density
distributions of stars and dark matter, stellar kinematics, and stellar
population properties, in the extended, low surface brightness halo regions of
elliptical galaxies. With integral field absorption spectroscopy and with
planetary nebulae as tracers, velocity dispersion and rotation profiles have
been followed to ~4 and ~5-8 effective radii, respectively, and in M87 to the
outer edge at ~150 kpc. The results are generally consistent with the known
dichotomy of elliptical galaxy types, but some galaxies show more complex
rotation profiles in their halos and there is a higher incidence of
misalignments, indicating triaxiality. Dynamical models have shown a range of
slopes for the total mass profiles, and that the inner dark matter densities in
ellipticals are higher than in spiral galaxies, indicating earlier assembly
redshifts. Analysis of the hot X-ray emitting gas in X-ray bright ellipticals
and comparison with dynamical mass determinations indicates that non-thermal
components to the pressure may be important in the inner ~10 kpc, and that the
properties of these systems are closely related to their group environments.
First results on the outer halo stellar population properties do not yet give a
clear picture. In the halo of one bright galaxy, lower [alpha/Fe] abundances
indicate longer star formation histories pointing towards late accretion of the
halo. This is consistent with independent evidence for on-going accretion, and
suggests a connection to the observed size evolution of elliptical galaxies
with redshift.Comment: 8 pages. Invited review to appear in the proceedings of "Galaxies and
their Masks" eds. Block, D.L., Freeman, K.C. & Puerari, I., 2010, Springer
(New York
3D-HST+CANDELS : the evolution of the galaxy size-mass distribution since z=3
Spectroscopic+photometric redshifts, stellar mass estimates, and rest-frame colors from the 3D-HST survey are combined with structural parameter measurements from CANDELS imaging to determine the galaxy size-mass distribution over the redshift range 0 < z < 3. Separating early- and late-type galaxies on the basis of star-formation activity, we confirm that early-type galaxies are on average smaller than late-type galaxies at all redshifts, and we find a significantly different rate of average size evolution at fixed galaxy mass, with fast evolution for the early-type population, R eff∝(1 + z)–1.48, and moderate evolution for the late-type population, R eff∝(1 + z)-0.75Peer reviewedFinal Accepted Versio
ZFOURGE catalogue of AGN candidates: an enhancement of 160-μm-derived star formation rates in active galaxies to z = 3.2
We investigate active galactic nuclei (AGN) candidates within the FourStar Galaxy Evolution Survey (ZFOURGE) to determine the impact they have on star formation in their host galaxies. We first identify a population of radio, X-ray, and infrared-selected AGN by cross-matching the deep Ks-band imaging of ZFOURGE with overlapping multiwavelength data. From this, we construct a mass-complete (log(M∗/M⊙M∗/M⊙) ≥9.75), AGN luminosity limited sample of 235 AGN hosts over z = 0.2–3.2. We compare the rest-frame U − V versus V − J (UVJ) colours and specific star formation rates (sSFRs) of the AGN hosts to a mass-matched control sample of inactive (non-AGN) galaxies. UVJ diagnostics reveal AGN tend to be hosted in a lower fraction of quiescent galaxies and a higher fraction of dusty galaxies than the control sample. Using 160 μm Herschel PACS data, we find the mean specific star formation rate of AGN hosts to be elevated by 0.34 ± 0.07 dex with respect to the control sample across all redshifts. This offset is primarily driven by infrared-selected AGN, where the mean sSFR is found to be elevated by as much as a factor of ∼5. The remaining population, comprised predominantly of X-ray AGN hosts, is found mostly consistent with inactive galaxies, exhibiting only a marginal elevation. We discuss scenarios that may explain these findings and postulate that AGN are less likely to be a dominant mechanism for moderating galaxy growth via quenching than has previously been suggested
Timing the Early Assembly of the Milky Way with the H3 Survey
The archeological record of stars in the Milky Way opens a uniquely detailed window into the early formation and assembly of galaxies. Here we use 11,000 main-sequence turn-off stars with well-measured ages, , , and orbits from the H3 Survey and Gaia to time the major events in the early Galaxy. Located beyond the Galactic plane, , this sample contains three chemically distinct groups: a low-metallicity population, and low-α and high-α groups at higher metallicity. The age and orbit distributions of these populations show that (1) the high-α group, which includes both disk stars and the in situ halo, has a star formation history independent of eccentricity that abruptly truncated 8.3 +- 0.1 Gyr ago (z sime 1); (2) the low-metallicity population, which we identify as the accreted stellar halo, is on eccentric orbits and its star formation truncated Gyr ago (z sime 2); (3) the low-α population is primarily on low-eccentricity orbits and the bulk of its stars formed less than 8 Gyr ago. These results suggest a scenario in which the Milky Way accreted a satellite galaxy at z ≈ 2 that merged with the early disk by z ≈ 1. This merger truncated star formation in the early high-α disk and perturbed a fraction of that disk onto halo-like orbits. The merger enabled the formation of a chemically distinct, low-α disk at z lesssim 1. The lack of any stars on halo-like orbits at younger ages indicates that this event was the last significant disturbance to the Milky Way disk
Near-Infrared Galaxy Counts to J and K ~ 24 as a Function of Image Size
We have used the Keck 10m telescope to count objects as a function of image
size in 2 high galactic latitude fields covering 1.5 arcmin^2 and reaching 50%
completeness at K=24 and J=24.5 for stellar sources. Counts extend ~1 mag
deeper in K than surveys with other telescopes; complement Keck surveys
providing counts at comparable or shallower depths but not utilizing image
structure; and extend by several magnitudes the J band counts from other
surveys. We find the surface-density of objects at K=23 to be higher than
previously found (~500,000/mag/deg^2), but at K<22 to be consistent with most
other surveys in amplitude and slope (~0.36). J band counts have similar slope.
J and K counts are in excess of our empirical no-evolution models for an open
universe, and a factor of 2 higher than mild-evolution models at J and K ~ 23.
The slope of the model counts is insensitive to geometry even in the
near-infrared because the counts are dominated by low-luminosity (<0.1L*)
objects at modest redshift (z<1) with small apparent sizes (r05<0.4", i.e. <4
kpc). The observed counts rise most steeply for these smaller objects, which
dominate fainter than K=22.3 and J=23.3. However, the greatest excess relative
to no-evolution models occurs for the apparently larger objects (median
J-K~1.5). The size and colors of such objects correspond equally well to
luminous (>0.1L*), galaxies at 1<z<4, or progressively more diffuse,
low-luminosity (0.001-0.1L*) galaxies at z<1. We rule out the excess is from
very low luminosity (<0.0001L*) red galaxies at z<0.25. There is a deficit of
galaxies with red J-K colors corresponding to luminous, early-type galaxies at
1<z<3. Assuming the deficit is due to their appearance as blue galaxies, they
account only for 10-30% of the excess of large, blue galaxies. [abridged]Comment: accepted for publication in ApJ; 34 pages text, 9 tables, 10 figures
(embedded); full resolution figures available at
http://www.astro.wisc.edu/~mab/publications/pub.htm
The Detailed Optical light Curve of GRB 030329
We present densely sampled BVRI light curves of the optical transient associated with the gamma-ray burst (GRB) 030329, the result of a coordinated observing campaign conducted at five observatories. Augmented with published observations of this GRB, theY. M.
Lipkin and E. O. Ofek are grateful to the Dan-David prize
foundation for financial support. A. Gal-Yam acknowledges
a Colton Fellowship. Y. M. Lipkin, E. O. Ofek, A. Gal-Yam,
D. Poznanski, and D. Polishook were supported in part
by grants from the Israel Science Foundation