Studies Of Galaxy Evolution Research Articles

The First Billion Years

The development of primordial inhomogeneities into the non-linear regime and the formation of the first astrophysical objects within low-mass (M ∼ 10 6 M ○. ) dark matter halos mark the end of the cosmic dark ages, about 150 Myr after the big bang. It is an early generation of extremely metal-poor stellar systems and accreting black holes in their nuclei that generated the ultraviolet/soft X-ray radiation and mechanical energy that reheated and reionized most of the hydrogen in the cosmos. The detailed thermal, ionization, and chemical enrichment history of the universe during the crucial formative stages around z = 10 - 30 depends on the power-spectrum of density fluctuations on small scales, on gas-phase H 2 astrochemistry, the stellar initial mass function and star formation efficiency, a complex network of poorly understood feedback mechanisms, and remains one of the crucial missing links in galaxy formation and evolution studies. In this talk I will review recent progress in understanding the epoch of first light, the impact of the earliest generation of luminous objects on later ones, and the hierarchical assembly of massive black holes from Population III seeds.

The Evolution of NGC 5128: Globular Clusters and Field Stars

AbstractAs the nearest giant elliptical galaxy, NGC 5128 (Centaurus A) is an excellent place to use globular clusters (GCs) and host galaxy field stars to study galaxy evolution. We have performed a detailed investigation of this galaxy, comparing field star kinematics with the metallicities, ages, and kinematics of GCs. We used our sample of 780 planetary nebulae (PNe) to trace the kinematics of the field star population. Our survey for GCs bring the total number of confirmed GCs to 215. Using spectra of the brightest GCs to determine ages, we find that the metal-rich GCs have a mean age of approximately 4-5 Gyr, and that their kinematics are similar to those of the PNe. The metal-poor GCs have old ages similar to the Galactic GCs, and show a weaker kinematic correlation with the field stars. It is possible that NGC 5128 was formed by the merger of two or more disk galaxies at the time that the metal-rich clusters were formed.

Spectroscopy of clusters in the ESO Distant Cluster Survey (EDisCS)

We present spectroscopic observations of galaxies in 4 clusters at z = 0.7-0.8 and in one cluster at z~0.5 obtained with the FORS2 spectrograph on the VLT as part of the ESO Distant Cluster Survey (EDisCS), a photometric and spectroscopic survey of 20 intermediate to high redshift clusters. We describe our target selection, mask design, observation and data reduction procedures, using these first 5 clusters to demonstrate how our strategies maximise the number of cluster members for which we obtain spectroscopy. We present catalogues containing positions, I-band magnitudes and spectroscopic redshifts for galaxies in the fields of our 5 clusters. These contain 236 cluster members, with the number of members per cluster ranging from 30 to 67. Our spectroscopic success rate, i.e. the fraction of spectroscopic targets which are cluster members, averages 50% and ranges from 30% to 75%. We use a robust biweight estimator to measure cluster velocity dispersions from our spectroscopic redshift samples. We also make a first assessment of substructure within our clusters. The velocity dispersions range from 400 to 1100 km s-1. Some of the redshift distributions are significantly non-Gaussian and we find evidence for significant substructure in two clusters, one at z~0.79 and the other at z~0.54. Both have velocity dispersions exceeding 1000 km s-1 but are clearly not fully virialised; their velocity dispersions may thus be a poor indicator of their masses. The properties of these first 5 EDisCS clusters span a wide range in redshift, velocity dispersion, richness and substructure, but are representative of the sample as a whole. Spectroscopy for the full dataset will allow a comprehensive study of galaxy evolution as a function of cluster environment and redshift.

Are passive spiral galaxies truly ‘passive’ and ‘spiral’? A near-infrared perspective

Passive spiral galaxies – unusual galaxies with spiral morphology without any sign of on-going star formation – have recently been found to exist preferentially in cluster infalling regions (at about the virial radius, or at a local galaxy density of ∼1 Mpc−2). The discovery directly connects passive spiral galaxies to cluster galaxy evolution studies such as the Butcher–Oemler effect or the morphology–density relation, i.e. passive spiral galaxies are likely to be transition objects between high-z blue, spiral galaxies and low-z red, cluster early-type galaxies. Thus, detailed study of passive spiral galaxies could potentially bring new insight into the underlying physical mechanisms governing cluster galaxy evolution. However, in previous work, passive spiral galaxies were selected from low-resolution optical images with ∼1.5 arcsec of seeing. Therefore, passive spirals could be a misidentification of S0 galaxies; or dusty starburst galaxies which are not passive at all. To answer these questions, we performed deep, high-resolution, near-infrared imaging of 32 passive spiral galaxies. Our high-resolution K-band images show clear spiral-arm structures. Thus, passive spirals are not S0s. Optical–infrared colour does not show any signs of dusty starburst at all. Therefore, it is likely that they are truly ‘passive’ and ‘spiral’ galaxies in the midst of cluster galaxy evolution.

Ultraviolet images of galaxies from the Optical Monitor on XMM-Newton

A large number of galaxies, both normal and active, have been observed in ultraviolet light by the Optical Monitor on XMM-Newton. These are some of the deepest wide-field ultraviolet images of these galaxies yet obtained, and in many cases the first collected in this waveband. We present images of five active galaxies, and discuss the potential uses of the ultraviolet surface brightness distribution and morphology, in association with X-ray data, for Active Galactic Nuclei, star formation and galaxy evolution studies.

A Reference Sample: ISM of the Most Isolated Galaxies

We are constructing the first complete unbiased control sample of the most isolated galaxies of the northern sky to serve as a template in the study of star formation and galaxy evolution in denser environments. Our goal is to compare and quantify the properties of different phases of the interstellar medium in this sample, as well as the level of star formation, both relevant parameters in the internal evolution of galaxies and strongly conditioned by the environment. To achieve this goal we are building a multiwavelength database for this sample to compare and quantify the properties of different phases of the ISM.

SCUBA-2: A large-format TES array for submillimetre astronomy

SCUBA-2, which replaces the Submillimetre Common User Bolometer Array (SCUBA) (Mon. Not. R. Astron. Soc. 303 (1999) 659) on the James Clerk Maxwell telescope in 2006, will be the first CCD-like array for submillimeter astronomy. Unlike previous detectors which have used discrete bolometers, SCUBA-2 has two DC-coupled, monolithic, filled arrays with a total of ∼10,000 bolometers. It will offer simultaneous imaging of an 8×8 arcmin field of view at wavelengths of 850 and 450μm. SCUBA-2 is expected to have a huge impact on the study of galaxy formation and evolution in the early Universe as well as star and planet formation in our own Galaxy. Mapping the sky to the same S/N up to 1000 times faster than SCUBA, it will also act as a pathfinder for the new submillimetre interferometers such as ALMA. SCUBA-2's absorber-coupled pixels use superconducting transition edge sensors (Ph.D. Thesis, Stanford, 1995) operating at ∼120mK for photon noise limited performance. The monolithic silicon detector arrays are deep-etched by the Bosch process to isolate the pixels on silicon nitride membranes (Nucl. Instr. and Meth. A, these proceedings). Electrical connections are made through indium bump bonds to a backplane that incorporates a SQUID time-domain multiplexer. We describe the key technologies that make SCUBA-2 possible and give an update on the considerable progress in the detector development and instrument design that has taken place over the last 2 years.

Hδ-Strong Galaxies in the Sloan Digital Sky Survey: I. The Catalog

Abstract We present here a new and homogeneous sample of 3340 galaxies selected from the Sloan Digital Sky Survey (SDSS) based solely on the observed strength of their $\mathrm{H}\delta$ hydrogen Balmer absorption line. The presence of a strong $\mathrm{H}\delta$ line within the spectrum of a galaxy indicates that the galaxy has undergone a significant change in its star-formation history within the last Gigayear. Therefore, such galaxies have received considerable attention in recent years, because they provide an opportunity to study galaxy evolution in action. These galaxies are commonly known as “post-starburst”, “E$+$A”, “k$+$a”, and $\mathrm{H}\delta$-strong galaxies. Their study has been severely hampered by the lack of a large, statistical sample of such galaxies. In this paper, we rectify this problem by selecting a sample of galaxies which possess an absorption $\mathrm{H}\delta$ equivalent width of $\mathrm{EW}(\mathrm{H}\delta_{\mathrm{max}})-\Delta \mathrm{EW}(\mathrm{H}\delta_{\mathrm{max}}) \gt 4 \,{Å}$$\mathrm{EW}(\mathrm{H}\delta_{\mathrm{max}})-\Delta \mathrm{EW}(\mathrm{H}\delta_{\mathrm{max}}) \gt 4 \,$Å from 106682 galaxies in the SDSS. The measured abundance of our $\mathrm{H}\delta$-strong (HDS) galaxies is $2.6 \pm 0.1 \%$ of all galaxies within a volume-limited sample of $0.05 < z < 0.1$ and $M_{r^{*}} <-20.5$, which is consistent with previous studies of such galaxies described in the literature. We find that only 25 of our HDS galaxies in this volume-limited sample ($3.5 \pm 0.7\%$) show no, or little, evidence for [O II] and $\mathrm{H}\alpha$ emission lines, thus indicating that true E$+$A galaxies (as originally defined by Dressler and Gunn) are extremely rare objects at low redshift, i.e., only $0.09 \pm 0.02\%$ of all galaxies in this volume-limited sample are true E$+$A galaxies. In contrast, $89 \pm 5\%$ of our HDS galaxies in the volume-limited sample have significant detections of the [O II] and $\mathrm{H}\alpha$ emission lines. Of these, only 131 galaxies are robustly classified as Active Galactic Nuclei (AGNs) and, therefore, a majority of these emission-line HDS galaxies are star-forming galaxies. We find that $52 \pm 12\%$ ($27/52$) of the galaxies in our volume-limited HDS sample that possess no detectable [O II] emission, do however possess detectable $\mathrm{H}\alpha$ emission lines. These may be dusty star-forming galaxies. We provide the community with this new catalog of $\mathrm{H}\delta$-strong galaxies to aid in our understanding of these galaxies, via detailed follow-up observations, as well as providing a low-redshift sample for comparison with higher redshift studies of HDS galaxies.

Re-ionization of the IGM — Massive Stars versus QSOs

In popular cold dark matter cosmological scenarios, stars may have first appeared in significant numbers around a redshift of 10 or so, as the gas within protogalactic halos with virial temperatures Tvir ≃ 20 000 K (corresponding to masses comparable to those of present-day dwarf ellipticals) cooled rapidly due to atomic processes and fragmented. It is this ‘second generation’ of subgalactic stellar systems, aided perhaps by an early population of accreting black holes in their nuclei, which may have generated the ultraviolet radiation and mechanical energy that ended the cosmic ‘dark ages’ and reheated and re-ionized most of the hydrogen in the universe by a redshift of z = 6. The detailed history of the universe during, and soon after these crucial formative stages, depends on the power-spectrum of density fluctuations on small scales and on a complex network of poorly understood feedback mechanisms, and is one of the missing links in galaxy formation and evolution studies.

Galaxy evolution from a microJansky radio survey

A strong evolution of galaxies is observed for 0<z<1, as evidenced by an increase of almost an order of magnitude in the galaxy star-formation rate density. However, it is known that dust obscuration has affected our understanding of galaxy evolution over this significant fraction of the age of the Universe. In order to study galaxy evolution free from dust induced biases, an ultra deep radio survey – the Phoenix Deep Survey – was initiated. With a detection limit of 60μJy, this homogeneous survey, complemented with multiwavelength (photometric and spectroscopic) observations, is being used to build a consistent picture of galaxy evolution. The ultra-deep radio source counts are presented, and interpreted using luminosity function evolutionary models. The discovery of extremely dusty galaxies from this survey, along with the clustering properties of the sub-mJy radio population, are also discussed.

GCD+: a new chemodynamical approach to modelling supernovae and chemical enrichment in elliptical galaxies

We have developed a new galactic chemo-dynamical evolution code, called GCD+, for studies of galaxy formation and evolution. This code is based on our original threedimensional tree N-body/smoothed particle hydrodynamics code which includes selfgravity, hydrodynamics, radiative cooling, star formation, supernova feedback, and metal enrichment. GCD+ includes a new Type II (SNe II) and Ia (SNe Ia) supernovae model taking into account the lifetime of progenitor stars, and chemical enrichment from intermediate mass stars. We apply GCD+ to simulations of elliptical galaxy formation, and examine the colour-magnitude relation (CMR), the Kormendy relation, and the [Mg/Fe]–magnitude relation of simulation end-products. GCD+ is a useful and unique tool which enables us to compare simulation results with the observational data directly and quantitatively. Our simulation confirm the results of Kawata (2001) who uses a simpler chemo-dynamical evolution code. We newly find that radiative cooling becomes more efficient and thus the gas infall rate increases,with decreasing mass of galaxies, which contributes to the slope of the CMR. In addition, the sophisticated treatments of both SNe II and SNe Ia in GCD+ show that feedback from SNe Ia plays a crucial role in the evolution of elliptical galaxies. We conclude that the feedback effect of SNe Ia should not be ignored in studying the evolution of elliptical galaxies.

Uncertainties of Synthetic Integrated Colors as Age Indicators

We investigate the uncertainties in the synthetic integrated colors of simple stellar populations. Three types of uncertainties are from the stellar models, the population synthesis techniques, and from the spectral libraries. Despite some skepticism, synthetic colors appear to be reliable age indicators when used for select age ranges. Rest-frame optical colors are good age indicators at ages 2 -- 7Gyr. At ages sufficiently large to produce hot HB stars, the UV-to-optical colors provide an alternative means for measuring ages. This UV technique may break the age-metallicity degeneracy because it separates old populations from young ones even in the lack of metallicity information. One can use such techniques on extragalactic globular clusters and perhaps even for high redshift galaxies that are passively evolving to study galaxy evolution history.

Disk galaxy evolution: from the Milky Way to high-redshift disks

We develop a detailed model of the Milky Way (a ``prototypical'' disk galaxy) and extend it to other disks with the help of some simple scaling relations, obtained in the framework of Cold Dark Matter models. This phenomenological (``hybrid'') approach to the study of disk galaxy evolution allows us to reproduce successfully a large number of observed properties of disk galaxies in the local Universe and up to redshift z~1. The important conclusion is that, on average, massive disks have formed the bulk of their stars earlier than their lower mass counterparts: the ``star formation hierarchy'' has been apparently opposite to the ``dark matter assembly'' hierarchy. It is not yet clear whether ``feedback'' (as used in semi-analytical models of galaxy evolution) can explain that discrepancy.

The K20 survey

The K20 survey is an ESO VLT optical and near-infrared spectroscopic survey aimed at obtaining spectral infor- mation and redshifts of a complete sample of about 550 objects to Ks 20:0 over two independent fields with a total area of 52 arcmin 2 . In this paper we discuss the scientific motivation of such a survey, we describe the photometric and spectroscopic properties of the sample, and we release the Ks-band photometric catalog. Extensive simulations showed that the sample is photometrically highly complete to Ks= 20. The observed galaxy counts and the R Ks color distribution are consistent with literature results. We observed spectroscopically 94% of the sample, reaching a spectroscopic redshift identification complete- ness of 92% to Ks 20:0 for the observed targets, and of 87% for the whole sample (i.e. counting also the unobserved targets). Deep spectroscopy was complemented with multi-band deep imaging in order to derive tested and reliable photometric red- shifts for the galaxies lacking spectroscopic redshifts. The results show a very good agreement between the spectroscopic and the photometric redshifts with = 0:01 and with a dispersion ofz= 0:09. Using both the spectroscopic and the photometric redshifts, we reached an overall redshift completeness of about 98%. The size of the sample, the redshift complete- ness, the availability of high quality photometric redshifts and multicolor spectral energy distributions make the K20 survey database one of the most complete samples available to date for constraining the currently competing scenarios of galaxy formation and for a variety of other galaxy evolution studies.

Optical (VRI) photometry in the field of the galaxy cluster AC 118 at $z=\mathsf{0.31}$

We present new photometric V-, R- and I-band data for the rich galaxy cluster AC 118 at z = 0.31. The new photometry covers an area of 8.6 x 8.6 arcmin 2 , corresponding to 2.9 x 2.9 Mpc 2 (H 0 = 50 km s - 1 Mpc - 1 , qo = 0.5 and A = 0). The data have been collected for a project aimed at studying galaxy evolution through the color-magnitude relation and the fundamental plane. We provide a catalogue including all the sources (N = 1206) detected in the cluster field. The galaxy sample is complete to V = 22.8 mag (N g a l = 574), R = 22.3 mag (N g a l = 649) and I = 20.8 mag (N g a l = 419). We give aperture magnitudes within a fixed aperture of 4.4 arcsec and Kron magnitudes. We also give photometric redshifts for 459 sources for which additional U- and K-band photometry is available. We derive and discuss the V- and R-band luminosity functions. The catalogue, which is distributed in electronic form, is intended as a tool for studies in galaxy evolution.

Metal-rich and Metal-poor Globular Clusters in Ellipticals: Did we Learn Anything? or Constraints on Galaxy Formation and Evolution from Globular Cluster Sub-populations

A brief review on globular cluster sub-populations in galaxies, and their constraints on galaxy formation and evolution is given. The metal-poor and metal-rich sub-populations are put in a historical context, and their properties, as known to date, are summarized. We review why the study of these sub-populations is extremely useful for the study of galaxy formation and evolution, but highlight a few caveats with the current interpretations. We re-visit the current globular cluster system formation scenarios and show how they boil down to a single scenario for the metal-poor clusters (namely the formation in “universal”, small fragments at high z) and that a hierarchical formation seems favored for the metal-rich clusters.

Galaxy colours in high-redshift, X-ray-selected clusters - I. Blue galaxy fractions in eight clusters

ABSTRA C T We present initial results from a wide-field, multicolour imaging project, designed to study galaxy evolution in X-ray-selected clusters at intermediate Oz , 0:25U and high redshifts Oz , 0:5U. We give blue galaxy fractions from eight X-ray-selected clusters, drawn from a combined sample of three X-ray surveys. We find that all the clusters exhibit excess blue galaxy populations over the numbers observed in local systems, although a large scatter is present in the results. We find no significant correlation of blue fraction with redshift at z . 0:2, although the large scatter could mask a positive trend. We also find no systematic trend of blue fraction with X-ray luminosity. We show that the blue fraction is a function of (a) radius within a cluster, (b) absolute magnitude and (c) the passbands used to measure the colour. We find that our blue fractions (fb) from galaxy colours close to rest frameOU 2 BU0, f b , 0:4, are systematically higher than those from rest frameOB 2 VU0 colours, f b , 0:2. We conclude this effect is real, may offer a partial explanation of the widely differing levels of blue fraction found in previous studies, and may have implications for biases in optical samples selected in different bands. While the increasing blue fraction with radius can be interpreted as evidence of cluster infall of field galaxies, the exact physical processes which these galaxies undergo is unclear. We estimate that, in the cores of the more massive clusters, galaxies should be experiencing ram-pressure stripping of galactic gas by the intracluster medium. The fact that our low X-ray luminosity systems show a similar blue fraction as the high-luminosity systems, as well as a significant blue fraction gradient with radius, implies other physical effects are also important.

Impact of Future Submillimeter and Millimeter Large Facilities on the Studies of Galaxy Formation and Evolution

ABSTRACTWe investigate what we can learn about galaxy formation and evolution from the data which will be obtained by the forthcoming large submillimeter/millimeter facilities, mainly by the Atacama Submillimeter Telescope Experiment (ASTE) and the Atacama Large Millimeter Array/Large Millimeter and Submillimeter Array (ALMA/LMSA). We first calculate the source counts from 350 μm to 3 mm using the empirical infrared galaxy number count model of Takeuchi et al. Based on the number counts, we evaluate the source confusion and determine the confusion limit at various wave bands as a function of the characteristic beam size. At submillimeter wavelengths, source confusion with the 10–15 m class facilities becomes severe at the 0.1–1 mJy level, and astrometry and flux measurements will be difficult. However, we show that a very large area survey of submillimeter sources brighter than 10–50 mJy can provide a unique constraint on infrared galaxy evolution at z = 1–2, and such a survey is suitable for the ASTE. In addition, such a survey enables us to study the clustering properties of submillimeter sources, which are still highly unknown. We also find that the 5 σ confusion limit of LMSA is fainter than 1 μJy, which enables us to study the contribution of sources at extremely large redshift. When we discuss such a deep flux limit, the dynamic range of a detector should be taken into account, since extremely bright sources make it impossible to detect the faintest sources near the detection limit. We evaluate the probability that sources that are 103 times brighter than the 5 σ detection limit of LMSA and ALMA exist in the field of view. We find that the probability is ≲3 × 10-4, and therefore we do not have to worry about the dynamic range. The source counts at such faint flux levels give important information about the epoch of galaxy formation. We then show that multiband photometry from the infrared (by ASTRO‐F) to the millimeter can be used as a redshift estimator. We examined the performance of this method by Monte Carlo simulations and found that it works successfully if we have reasonable measurement accuracy. In addition, we compare the observed 1.4, 5, and 8 GHz source counts with our model counts to examine the contribution of star‐forming galaxies to faint radio galaxies. We find that the faintest radio number counts (∼1 μJy) are dominated by actively star‐forming galaxies which lie at intermediate redshift z∼1–2.

The Radio Galaxy Populations of Nearby Northern Abell Clusters

We report on the use of the NRAO VLA Sky Survey (NVSS) to identify radio galaxies in 18 nearby Abell clusters. The listings extend from the cores of the clusters out to radii of 3 h Mpc, which corresponds to 1.5 Abell radii and approximately 4 orders of magnitude in galaxy density. To create a truly useful catalog, we have collected optical spectra for nearly all of the galaxies lacking public velocity measurements. Consequently, we are able to discriminate between those radio galaxies seen in projection on the cluster and those that are in actuality cluster members. The resulting catalog consists of 329 cluster radio galaxies plus 138 galaxies deemed foreground or background objects, and new velocity measurements are reported for 273 of these radio galaxies. The motivation for the catalog is the study of galaxy evolution in the cluster environment. The radio luminosity function is a powerful tool in the identification of active galaxies, as it is dominated by star-forming galaxies at intermediate luminosities and active galactic nuclei (AGNs) at higher luminosities. The flux limit of the NVSS allows us to identify AGNs and star-forming galaxies down to star formation rates less than 1 M☉ yr-1. This sensitivity, coupled with the all-sky nature of the NVSS, allows us to produce a catalog of considerable depth and breadth. In addition to these data, we report detected infrared fluxes and upper limits obtained from IRAS data. It is hoped that this database will prove useful in a number of potential studies of the effect of environment on galaxy evolution.

Stellar Populations in BL Lac type Objects

The relationship between an Active Galactic Nucleus (AGN) and its host galaxy is a crucial question in the study of galaxy evolution. We present an estimate of the stellar contribution in a sample of low luminosity BL Lac type objects. We have performed stellar population synthesis for a sample of 19 objects selected from Marcha et al. (1996, MNRAS 281, 425). The stellar content is quantified using the equivalent widths of all absorption features available throughout the spectrum. The synthesis is done by a variant of the GPG method (Pelat: 1997, MNRAS 284, 365).