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A. E. Shapley

Publications and source records attributed to A. E. Shapley.

50 records · Page 3Linked to original sources
arXiv2006

SINFONI Integral Field Spectroscopy of z~2 UV-selected Galaxies: Rotation Curves and Dynamical Evolution

We present 0.5" resolution near-IR integral field spectroscopy of the Ha line emission of 14 z~2 UV-selected BM/BX galaxies obtained with SINFONI at ESO/VLT. The mean Ha half-light radius r_1/2 is about 4kpc and line emission is detected over > ~20kpc in several sources. In 9 sources, we detect spatially-resolved velocity gradients, from 40 to 410 km/s over ~10kpc. The observed kinematics of the larger systems are consistent with orbital motions. Four galaxies are well described by rotating disks with clumpy morphologies and we extract rotation curves out to radii > ~10kpc. One or two galaxies exhibit signatures more consistent with mergers. Analyzing all 14 galaxies in the framework of rotating disks, we infer mean inclination- and beam-corrected maximum circular velocities v_c of 180+-90 km/s and dynamical masses of (0.5-25)x10^10 Msun within r_1/2. On average, the dynamical masses are consistent with photometric stellar masses assuming a Chabrier/Kroupa IMF but too small for a 0.1-100 Msun Salpeter IMF. The specific angular momenta of our BM/BX galaxies are similar to those of local late-type galaxies. The specific angular momenta of their baryons are comparable to those of their dark matter halos. Extrapolating from the average v_c at 10kpc, the virial mass of the typical halo of a galaxy in our sample is 10^(11.7+-0.5) Msun. Kinematic modeling of the 3 best cases implies a ratio of v_c to local velocity dispersion of order 2-4 and accordingly a large geometric thickness. We argue that this suggests a mass accretion (alternatively, gas exhaustion) timescale of ~500Myr. We also argue that if our BM/BX galaxies were initially gas rich, their clumpy disks will subsequently lose their angular momentum and form compact bulges on a timescale of ~1 Gyr. [ABRIDGED]

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arXiv2005

The Connection Between Galaxies and Intergalactic Absorption Lines at Redshift 2<z<3

Absorption-line spectroscopy of 23 background QSOs and numerous background galaxies has let us measure the spatial distribution of metals and neutral hydrogen around 1044 UV-selected galaxies at redshifts 1.8 260 km/s) and produces very strong absorption lines (N_CIV >> 10^14 cm^-2) in the spectra of background objects. Absorption with an average column density of N_CIV ~ 10^14 cm^-2 extends to 80 kpc, a radius large enough to imply that most strong intergalactic CIV absorption is associated with star-forming galaxies like those in our sample. We find that the galaxy-CIV cross-correlation length increases with CIV column density and is similar to the galaxy-galaxy length (r_0 ~ 4 h^-1 Mpc) for N_CIV > 10^12.5 cm^-2. Distortions in the redshift-space galaxy-CIV correlation function on small scales may imply that some of the CIV systems have large peculiar velocities. Four of the five detected OVI absorption systems in our sample lie within 400 proper kpc of a known galaxy. Strong Lyman-a absorption is produced by the intergalactic gas within 1 h^-1 comoving Mpc of most galaxies, but for a significant minority (~1/3) the absorption is weak or absent. We were unable to identify any statistically significant differences between galaxies with weak nearby HI absorption and the rest, although galaxies with weak absorption may have higher star-formation rates. Galaxies near intergalactic CIV systems appear to reside in relatively dense environments and to have distinctive spectral energy distributions that are characterized by blue colors and young ages. (abridged)

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arXiv2004

The Spatial Clustering of Star-forming Galaxies at Redshifts 1.4<z<3.5

We analyzed the spatial distribution of 28500 photometrically selected galaxies with AB magnitude 23.5<R<25.5 and redshift 1.4<z<3.5 in 21 fields with a total area of 0.81 square degrees. The galaxies were divided into three subsamples, with mean redshifts z=1.7, 2.2, 2.9, according to the UGR selection criteria of Adelberger et al. (2004) and Steidel et al. (2003). Combining the galaxies' measured angular clustering with redshift distributions inferred from 1600 spectroscopic redshifts, we find comoving correlation lengths at the three redshifts of r_0 = 4.5+-0.6, 4.2+-0.5, and 4.0+-0.6 h^-1 Mpc, respectively, and infer a roughly constant correlation function slope of gamma=1.6+-0.1. We derive similar numbers from the 1600 object spectroscopic sample itself with a new statistic, K, that is insensitive to many possible systematics. Galaxies that are bright in R (lambda_rest ~ 1500-2500A) cluster more strongly than fainter galaxies at z=2.9 and z=2.2 but not, apparently, at z=1.7. Comparison to a numerical simulation that is consistent with recent WMAP observations suggests that galaxies in our samples are associated with dark matter halos of mass ~ 10^12, and that a small fraction of the halos contain more than one galaxy that satisfies our selection criteria. Adding recent observations of galaxy clustering at z~0 and z~1 to the simulation results, we conclude that the typical object in our samples will evolve into an elliptical galaxy by redshift z=0 and will already have an early-type spectrum by redshift z=1. We comment briefly on the implied relationship between galaxies in our survey and those selected with other techniques. (slightly abridged)

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arXiv2004

Deep mid-infrared observations of Lyman-break galaxies

As part of the In-Orbit Checkout activities for the Spitzer Space Telescope, the IRAC team carried out a deep observation (average integration time ~8 hours) of a field surrounding the bright QSO HS 1700+6416. This field contains several hundred z~3 Lyman-break galaxy candidates, and we report here on their mid-infrared properties, including the IRAC detection rate, flux densities and colors, and the results of fitting population synthesis models to the optical, near-infrared, and IRAC magnitudes. The results of the model-fitting show that previous optical/near-infrared studies of LBGs were not missing large, hidden old stellar populations. The LBG candidates' properties are consistent with those of massive, star-forming galaxies at z~3. Other IRAC sources in the same field have similar properties, so IRAC selection may prove a promising method of finding additional high-redshift galaxies.

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arXiv2004

A Survey of Star-Forming Galaxies in the z=1.4-2.5 `Redshift Desert': Overview

We present the first results of a large-scale survey, using the UV/blue sensitive LRIS-B spectrograph on the Keck I telescope, of galaxies in the redshift interval 1.4 =2.20+/-0.32 and `BM' galaxies at =1.70+/-0.34; currently we have spectroscopically confirmed 749 of the former and 114 of the latter. We also present initial results of deep near-IR photometry and spectroscopy, from which we show that z~2 galaxies are significantly redder in their optical/IR colors compared to similarly UV-selected galaxies at z~3, but that the characteristics of their galaxy-scale outflows are quite similar. We illustrate by example the information which can be deduced on the stellar populations, metallicities, and kinematics of `redshift desert' galaxies from easily accessible rest-frame far-UV and rest-frame optical spectra. Far from being hostile to observations, the universe at z~2 is uniquely suited to providing information on the astrophysics of star-forming galaxies and the intergalactic medium, and the relationship between the two [abridged].

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arXiv2003

Lyman Break Galaxies at Redshift z~3: Survey Description and Full Data Set

We present the basic data for a large ground-based spectroscopic survey for z~3 ``Lyman break galaxies'' (LBGs), photometrically selected using rest-UV colors from very deep images in 17 high Galactic latitude fields. The total survey covers an area of 0.38 square degrees, and includes 2347 photometrically-selected candidate LBGs to an apparent R_{AB} magnitude limit of 25.5. Approximately half of these objects have been observed spectroscopically using the Keck telescopes, yielding 940 redshifts with =2.96 +/- 0.29. We discuss the images, photometry, target selection, and the spectroscopic program in some detail, and present catalogs of the photometric and spectroscopic data, made available in electronic form. We discuss the general utility of conducting nearly-volume-limited redshift surveys in prescribed redshift intervals using judicious application of photometric pre-selection.

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arXiv2003

Rest-Frame Ultraviolet Spectra of z~3 Lyman Break Galaxies

We present the results of a systematic study of the rest-frame UV spectroscopic properties of Lyman Break Galaxies (LBGs). The database of almost 1000 LBG spectra proves useful for constructing high S/N composite spectra. The composite spectrum of the entire sample reveals a wealth of features attributable to hot stars, HII regions, dust, and outflowing neutral and ionized gas. By grouping the database according to galaxy parameters such as Lyman-alpha equivalent width, UV spectral slope, and interstellar kinematics, we isolate some of the major trends in LBG spectra which are least compromised by selection effects. We find that LBGs with stronger Lyman-alpha emission have bluer UV continua, weaker low-ionization interstellar absorption lines, smaller kinematic offsets between Lyman-alpha and the interstellar absorption lines, and lower star-formation rates. There is a decoupling between the dependence of low- and high-ionization outflow features on other spectral properties. Most of the above trends can be explained in terms of the properties of the large-scale outflows seen in LBGs. According to this scenario, the appearance of LBG spectra is determined by a combination of the covering fraction of outflowing neutral gas which contains dust, and the range of velocities over which this gas is absorbing. Higher sensitivity and spectral resolution observations are still required for a full understanding of the covering fraction and velocity dispersion of the outflowing neutral gas in LBGs, and its relationship to the escape fraction of Lyman continuum radiation in galaxies at z~3.

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arXiv2002

Galaxies and Intergalactic Matter at Redshift z~3: Overview

We present the first results from a survey of the relative spatial distributions of galaxies, intergalactic neutral hydrogen, and intergalactic metals at high redshift. We obtained high-resolution spectra of 8 bright QSOs at 3.1<z<4.1 and spectroscopic redshifts for 431 Lyman-break galaxies (LBGs) at slightly lower redshifts. Comparing the locations of galaxies to the absorption lines in the QSO spectra shows that the intergalactic medium contains less neutral hydrogen than the global average within r<0.5h^-1 comoving Mpc of LBGs and more than average at slightly larger distances 1<r<5 h^-1 comoving Mpc. The intergalactic medium within the largest overdensities at z~3, which will presumably evolve into the intracluster medium by z~0, is rich in neutral hydrogen and CIV. The lack of HI absorption at small distances from LBGs appears unlikely to be produced solely by the Lyman continuum radiation they emit; it may show that the galaxies' supernovae-driven winds maintain their measured outflow velocities of ~600 km/s for a few hundred million years and drive away nearby intergalactic gas. We present correlation functions of galaxies with Lyman-alpha forest flux decrements, with CIV systems, and with other galaxies. We describe the association of galaxies with damped Lyman-a systems and with intergalactic HeII opacity. A strong observed correlation of galaxies with intergalactic metals supports the idea that Lyman-break galaxies' winds have enriched their surroundings.

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arXiv2002

The Kinematic Connection Between QSO-Absorbing Gas and Galaxies at Intermediate Redshift

We present complementary data on 5 intermediate redshift (0.44 < z < 0.66) MgII absorbing galaxies, combining high spatial resolution imaging from HST, high--resolution QSO spectroscopy from Keck/HIRES, and galaxy kinematics from intermediate resolution spectroscopy using Keck/LRIS. These data allow a direct comparison of the kinematics of gas at large galactocentric impact parameters with the galaxy kinematics obtained from the faint galaxy spectroscopy. All 5 galaxies appear to be relatively normal spirals, with measured rotation curves yielding circular velocities in the range 100 < v_c < 260 km/s. We find that in 4 of the 5 cases examined, the velocities of all of the Mg II absorption components lie entirely to one side of the galaxy systemic redshift. These observations are consistent with rotation being dominant for the absorbing gas kinematics; however, the total range of velocities observed is inconsistent with simple disk rotation in every case. Simple kinematic models that simultaneously explain both the systemic offset of the absorbing material relative to the galaxy redshifts, and the total velocity width spanned by the absorption, require either extremely thick rotating gas layers, rotation velocities that vary with height above the extrapolation of the galactic plane, or both. In any case, our small sample suggests that rotating ``halo'' gas is a common feature of intermediate redshift spiral galaxies, and that the kinematic signature of rotation dominates over radial infall or outflow even for gas well away from the galactic plane. We discuss possible explanations for this behavior, and compare our observations to possible local analogs.

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arXiv2001

Physical Conditions in Lyman Break Galaxies Derived From Rest-Frame UV Spectra

We present the results of detailed studies of the astrophysical conditions in z~3 Lyman Break Galaxies (LBGs), placing particular emphasis on what is learned from LBG rest frame UV spectra. By drawing from our database of ~1000 spectra, and constructing higher S/N composite spectra from galaxies grouped according to properties such as luminosity, extinction, morphology, and environment, we can show how the rest-frame UV spectroscopic properties systematically depend on other galaxy properties. Such information is crucial to understanding the detailed nature of LBGs, and their impact on the surrounding IGM.

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arXiv2001

The Rest-Frame Optical Properties of z~3 Galaxies

We present the results of a near-infrared imaging survey of z~3 Lyman Break Galaxies (LBGs). The survey covers a total of 30 arcmin^2 and includes 118 photometrically selected LBGs with K_s band measurements, 63 of which also have J band measurements, and 81 of which have spectroscopic redshifts. Using the distribution of optical {\cal R} magnitudes from previous work and {\cal R}-K_s colors for this sub-sample, we compute the rest-frame optical luminosity function of LBGs. At the brightest magnitudes, where it is fairly well constrained, this luminosity function strikingly exceeds locally determined optical luminosity functions. The V-band luminosity density of only the observed bright end of the z~3 LBG luminosity function already approaches that of all stars in the local universe. For the 81 galaxies with measured redshifts, we investigate the range of LBG stellar populations implied by the photometry which generally spans the range 900--5500 AA in the rest-frame. While there are only weak constraints on the parameters for most of the individual galaxies, there are strong trends in the sample as a whole. A unified scenario which accounts for the observed trends in bright LBGs is one in which a relatively short period of very rapid star-formation (hundreds of M_sun/yr) lasts for roughly 50--100 Myr, after which both the extinction and star-formation rate are considerably reduced and stars are formed at a more quiescent, but still rapid, rate for at least a few hundred Myr. In our sample, a considerable fraction (~20%) of the LBGs have best-fit star-formation ages ~> 1 Gyr, implied stellar masses of ~> 10^10 M_sun, and are still forming stars at \~30 M_sun/yr.

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arXiv2000

Sub-mm imaging of a proto-cluster region at z=3.09

We have used the Submillimetre Common-User Bolometer Array (SCUBA) detector on the James Clerk Maxwell Telescope (JCMT) to measure bright sub-mm emission associated with a recently discovered extensive (>100/h kpc) and highly luminous, `blob' of Ly-alpha emission at z=3.09. The blob lies within a known large overdensity of optical sources in the z=3.07-3.11 range, and is centered on a locally overdense peak within this region. The best explanation for the copious sub-mm emission is a dust obscured continuum source, which may produce the ionizing flux for the Ly-alpha cloud. Cooling gas explanations are plausible but excessively complicated, and the 450/850 micron ratio rules out a significant fraction of the signal arising from the Sunyaev-Zel'dovich increment. At least two additional ~10 mJy sub-mm detections in the SCUBA map, with a surface density significantly higher than in blank field surveys, suggests that they may be associated with the z=3.09 structure. A SCUBA `photometry' observation of a second nearby Ly-alpha blob tentatively detects a weaker sub-mm counterpart.

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arXiv1999

Lyman Alpha Imaging of a Proto-Cluster Region at =3.09

We present very deep imaging observations, through a narrow-band filter tuned to Lyman alpha at , of a volume containing a significant over-density of galaxies at this redshift previously discovered in our survey for continuum-selected Lyman break galaxies (LBGs). The new observations are used in conjunction with our spectroscopic results on LBGs to compare the effectiveness of continuum and emission line searches for star forming galaxies at high redshift, and to extend the search for members of the structure at = 3.09 to much fainter continuum luminosities. We find that only 20-25 percent of all galaxies at a given UV continuum luminosity would be flagged as narrow-band excess objects subject to the typical limits W_Lya > 80 Angstroms in the observed frame. The density enhancement of strong Lyman alpha emitters in this field is consistent with that inferred from the analysis of the spectroscopic Lyman break galaxy sample in the same region (6+/-1), but extends to continuum luminosities up to 2 magnitudes fainter. There is no evidence for a significantly higher fraction of large Lyman alpha line equivalent widths at faint continuum luminosities. By combining the 24 spectroscopic members of the z=3.09 ``spike'' with the narrow-band candidates, we are able to produce a sample of 162 objects which are either known or likely members of this large structure. We have also discovered two extremely large and diffuse Lyman alpha emitting ``blobs'', which have physical extents >100/h kpc and Lyman alpha line fluxes 20-40 times larger than the typical line emitters at the same redshifts in the field. The possible nature of the ``blobs'' is discussed. (abstract abridged)

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