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K. L. Adelberger

Publications and source records attributed to K. L. Adelberger.

At least 19 recordsLinked to original sources
arXiv2005

Possible Detection of Lyman-alpha Fluorescence from a Damped Lyman Alpha system at Redshift z=2.8

We have detected Lyman-alpha emission from a damped Lyman-alpha system (DLA) that lies near the bright quasar HS1549+1919. The DLA has the same redshift as HS1549+1919 and was discovered in the spectrum of a faint QSO that lies 49" away (380 proper kpc). The emission line's luminosity, double-peaked profile, and small spatial separation from the DLA suggest that it may be fluorescent Lyman-alpha emission from gas that is absorbing the nearby QSO's radiation. If this is the case, our observations show that the DLA has a size of at least 1.5" and that the QSO's luminosity one million years ago was similar to its luminosity today. A survey for similar systems within 1' of bright QSOs would put interesting limits on the mean quasar lifetime.

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arXiv2005

Constraints from Galaxy-AGN Clustering on the Correlation between Galaxy and Black Hole Mass at Redshifts 2<Z<3

We use the clustering of galaxies around distant active-galactic nuclei to derive an estimate of the relationship between galaxy and black hole mass that obtained during the ancient quasar epoch, at redshifts 2 <~ z <~ 3, when giant black holes accreted much of their mass. Neither the mean relationship nor its scatter differs significantly from what is observed in the local universe, at least over the ranges of apparent magnitude (16 <~ G_AB <~ 26) and black-hole mass (10^6 <~ M_BH/M_sun <~ 10^10.5) that we are able to probe.

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arXiv2005

A Possible Correlation Between the Luminosities and Lifetimes of Active Galactic Nuclei

We use the clustering of galaxies around distant AGN to show with ~90% confidence that fainter AGN are longer lived. Our argument is simple: since the measured galaxy-AGN cross-correlation length r_0 ~ 5h^-1 Mpc does not vary significantly over a 10 magnitude range in AGN optical luminosity, faint and bright AGN must reside in dark matter halos with similar masses. The halos that host bright and faint AGN therefore have similar intrinsic abundances, and the large observed variation in AGN number density with luminosity reflects a change in duty cycle.

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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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arXiv2005

X-ray properties of UV-selected star forming galaxies at z~1 in the Hubble Deep Field North

We present an analysis of the X-ray emission from a large sample of ultraviolet (UV) selected, star forming galaxies with 0.74<z<1.32 in the Hubble Deep Field North (HDF-N) region. By excluding all sources with significant detected X-ray emission in the 2 Ms Chandra observation we are able to examine the properties of galaxies for which the emission in both UV and X-ray is expected to be predominantly due to star formation. Stacking the X-ray flux from 216 galaxies in the soft and hard bands produces significant detections. The derived mean 2-10 keV rest-frame luminosity is 2.97+/-0.26x10^(40) erg/s, corresponding to an X-ray derived star formation rate (SFR) of 6.0+/-0.6 Msolar/yr. Comparing the X-ray value with the mean UV derived SFR, uncorrected for attenuation, we find that the average UV attenuation correction factor is \~3. By binning the galaxy sample according to UV magnitude and colour, correlations between UV and X-ray emission are also examined. We find a strong positive correlation between X-ray emission and rest-frame UV emission. A correlation between the ratio of X-ray-to-UV emission and UV colour is also seen, such that L(X)/L(UV) increases for redder galaxies. Given that X-ray emission offers a view of star formation regions that is relatively unaffected by extinction, results such as these can be used to evaluate the effects of dust on the UV emission from high-z galaxies. For instance we derive a relationship for estimating UV attenuation corrections as a function of colour excess. The observed relation is inconsistent with the Calzetti et al. (2000) reddening law which over predicts the range in UV attenuation corrections by a factor of ~100 for the UV selected z~1 galaxies in this sample (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

Measuring the Influence of Supernovae at High Redshift

Supernovae play a large but poorly understood role in our attempts to explain the evolution of the baryonic universe. Numerous observations throughout astronomy cannot be explained if we neglect their influence, yet our quantitative understanding of the ways in which supernovae affect the universe remains remarkably poor. This is one of the most embarrassing gaps in our knowledge of the cosmos, and planned telescopes and surveys will probably not do much to fill it. The problem is that these surveys will be optimized to observe galaxies and intergalactic material independently of each other, while (in the author's view) by far the best information will come from simultaneous surveys of galaxies and the intergalactic material (IGM) in their vicinity. Only this will show directly how galaxies affect their surroundings and provide a rough energy scale for supernova-driven winds. Redshifts 1<z<3 are ideal for the joint galaxy/IGM surveys we advocate, because the comoving density of star formation is near its peak, because the Lyman-alpha forest is thin enough for QSO spectra to reveal the locations of the dominant metallic species, and because bright background QSOs are common. But a new UV-capable spectrograph in space will be required.

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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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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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arXiv2001

The Cosmic Star-Formation History: The UV finds most

This is a summary of arguments in favor of observing high-redshift star formation in the UV as presented at the Ringberg meeting in September 2000. The most rapidly star-forming galaxies are very dusty, easier to detect at 850um than in the UV, but less rapidly star-forming galaxies are less obscured by dust and as a result the comparatively faint galaxies that hosted most high-redshift star formation are easiest to detect in the UV. The correlation of star-formation rate and dust obscuration implies that extremely luminous dusty galaxies are usually as bright in the UV as the less luminous dust-free galaxies, and that any UV survey at a given redshift 0<z<~3 deep enough to detect the majority of the UV luminosity density will detect the majority of IR-selected galaxies as well. Little star formation occurs in galaxies that are completely hidden from UV surveys. I review recent attempts to estimate star-formation rates for high-redshift galaxies from UV data alone. The strength of UV surveys is that they detect large numbers of high-redshift galaxies, even ones that are intrinsically very faint, in large and representative comoving volumes. The weakness is that star-formation rates are difficult to estimate for the detected galaxies. IR surveys complement them perfectly: star-formation rates can be estimated with reasonable confidence, but only small regions of the sky can be surveyed and only the most luminous sources can be detected. Multiwavelength cooperation, not conflict, will lead to future progress in this field.

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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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arXiv2000

Multi-wavelength Observations of Dusty Star Formation at Low and High Redshift

This paper examines what can be learned about high-redshift star formation from the small fraction of high-redshift galaxies' luminosities that is emitted at accessible wavelengths. We review and quantify empirical correlations between bolometric luminosities produced by star formation and the UV, mid-IR, sub-mm, and radio luminosities of galaxies in the local universe. These correlations suggest that observations of high-redshift galaxies at any of these wavelengths should constrain their star-formation rates to within 0.2--0.3 dex. We assemble the limited evidence that high-redshift galaxies obey these locally calibrated correlations. The characteristic luminosities and dust obscurations of galaxies at z ~ 0, z ~ 1, and z ~ 3 are reviewed. After discussing the relationship between the high-redshift populations selected in surveys at different wavelengths, we calculate the contribution to the 850um background from each. The available data show that a correlation between star-formation rate and dust obscuration L_dust/L_UV exists at low and high redshift. This correlation plays a central role in the major conclusion of this paper: most star formation at high redshift occurred in galaxies with 1 < L_dust/L_UV < 100 similar to those that host the majority of star formation in the local universe and to those that are detected in UV-selected surveys. (abridged)

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