Studies Of Galaxy Evolution Research Articles

Dynamical Models of Elliptical Galaxies inz = 0.5 Clusters. II. Mass‐to‐Light Ratio Evolution without Fundamental Plane Assumptions

We study M/L evolution of early-type galaxies using dynamical modeling of resolved internal kinematics. This makes fewer assumptions than Fundamental Plane (FP) studies and provides a powerful new approach for studying galaxy evolution. We focus on the sample of 25 galaxies in clusters at z=0.5 modeled in Paper I. For comparison we compile and homogenize M/L literature data for 60 nearby galaxies that were modeled in comparable detail. The nearby sample obeys log(M/L)_B = Z + S log(sigma_eff/[200 km/s]), with Z = 0.896 +/- 0.010, S = 0.992 +/- 0.054, and sigma_eff the effective velocity dispersion. The z=0.5 sample follows a similar relation but with lower zeropoint. The implied M/L evolution is Delta log(M/L) / Delta z = -0.457 +/- 0.046(random) +/- 0.078(systematic), consistent with passive evolution following high-redshift formation. This agrees with the FP results for this sample by van Dokkum & van der Marel. This confirms that FP evolution tracks M/L evolution, which is an important verification of the assumptions that underly FP studies. However, while we find more FP evolution for galaxies of low sigma_eff (or low mass), the dynamical M/L evolution instead shows little trend with sigma_eff. We argue that this difference can be plausibly attributed to a combination of two effects: (a) evolution in structural galaxy properties other than M/L; and (b) the neglect of rotational support in studies of FP evolution. The results leave the question open whether the low-mass galaxies in the sample have younger population ages than the high-mass galaxies. This highlights the general importance in the study of population ages for complementing dynamical measurements with broad-band colors or spectroscopic population diagnostics.

The ALFALFA Search for (Almost) Dark Galaxies across the HI Mass Function

AbstractThe Arecibo Legacy Fast ALFA (ALFALFA) survey is a second generation blind extragalactic HI survey currently in progess which is exploiting Arecibo's superior sensitivity, angular resolution and digital technology to derive a census of the local HI universe over a cosmologically significant volume. As of the time of this meeting, some 4500 good quality extragalactic HI line sources have been identified in about 15% of the final survey area. ALFALFA is detecting HI masses as low as 106M⊙and as large as 1010.8M⊙with positional accuracies typically better than 20″, allowing immediate identification of the most probable optical counterparts. Only 3% of all extragalactic HI sources and less than 1% of detections withMH I> 109.5M⊙cannot be identified with a stellar component. Because ALFALFA is far from complete, the discussion here focuses on limitations of past surveys that ALFALFA will overcome because of its greater volume, sensitivity and reduced susceptibility to source confusion and on a sampling of illustrative preliminary results. First ALFALFA results already suggest, in agreement with previous studies, that there does not appear to be a cosmologically significant population of optically dark but HI rich galaxies. ALFALFA promises a wealthy dataset for the exploration of many issues in near-field cosmology and galaxy evolution studies, setting the stage for their extension to higher redshifts in the future with the Square Kilometer Array (SKA).

A study of catalogued nearby galaxy clusters in the SDSS-DR4

Context.Large surveys such as the Sloan Digital Sky Survey have made large amounts of spectroscopic and photometric data of galaxies available, thereby providing important information for studying galaxy evolution in dense environments.

The FALCON concept: multi-object adaptive optics and atmospheric tomography for integral field spectroscopy - principles and performance on an 8-m telescope

Integral field spectrographs are major instruments with which to study the mechanisms involved in the formation and the evolution of early galaxies. When combined with multi-object spectroscopy, those spectrographs can behave as machines used to derive physical parameters of galaxies during their formation process. Up to now, there has been only one available spectrograph with multiple integral field units, i.e. FLAMES/GIRAFFE on the European Southern Observatory (ESO) Very Large Telescope (VLT). However, current ground-based instruments suffer from a degradation of their spatial resolution due to atmospheric turbulence. In this article we describe the performance of FALCON, an original concept of a new-generation multi-object integral field spectrograph with adaptive optics for the ESO VLT. The goal of FALCON is to combine high angular resolution (0.25 arcsec) and high spectral resolution (R > 5000) in the J and H bands over a wide field of view (10 x 10 arcmin 2 ) in the VLT Nasmyth focal plane. However, instead of correcting the whole field, FALCON will use multi-object adaptive optics (MOAO) to perform the adaptive optics correction locally on each scientific target. This requires us then to use atmospheric tomography in order to use suitable natural guide stars for wavefront sensing. We will show that merging MOAO and atmospheric tomography allows us to determine the internal kinematics of distant galaxies up to z ≈ 2 with a sky coverage of 50 per cent, even for objects observed near the Galactic pole. The application of such a concept to extremely large telescopes seems therefore to be a very promising way to study galaxy evolution from z = 1 to redshifts as high as z = 7.

Uncovering the chemical enrichment and mass-assembly histories of star-forming galaxies

Abstract We explore the mass-assembly and chemical enrichment histories of star-forming galaxies by applying a population synthesis method to a sample of 84828 galaxies from the Sloan Digital Sky Survey Data Release 5. Our method decomposes the entire observed spectrum in terms of a sum of simple stellar populations spanning a wide range of ages and metallicities, thus allowing the reconstruction of galaxy histories. A comparative study of galaxy evolution is presented, where galaxies are grouped on to bins of nebular abundances or mass. We find that galaxies whose warm interstellar medium is poor in heavy elements are slow in forming stars. Their stellar metallicities also rise slowly with time, reaching their current values (Z★∼ 1/3Z⊙) in the last ∼100 Myr of evolution. Systems with metal-rich nebulae, on the other hand, assembled most of their mass and completed their chemical evolution long ago, reaching Z★∼ Z⊙ at lookback times of several Gyr. These same trends, which are ultimately a consequence of galaxy downsizing, appear when galaxies are grouped according to their stellar mass. The reconstruction of galaxy histories to this level of detail out of integrated spectra offers promising prospects in the field of galaxy evolution theories.

A new (2+1)D cluster finding algorithm based on photometric redshifts: large scale structure in the Chandra deep field south

Aims: We study galaxy clustering and explore the dependence of galaxy properties on the the environment up to a redshift z~1, on the basis of a deep multi-band survey in the Chandra Deep Field South. Methods: We have developed a new method which combines galaxy angular positions and photometric redshifts to estimate the local galaxy number-density. This allows both the detection of overdensities in the galaxy distribution and the study of the properties of the galaxy population as a function of the environmental density. Results: We detect two moderate overdensities at z~0.7 and z~1 previously identified spectroscopically. We find that the fraction of red galaxies within each structure increases with volume density, extending to z~1 previous results. We measure ``red sequence'' slopes consistent with the values found in X-ray selected clusters, supporting the notion that the mass-metallicity relation hold constant up to z~1. Conclusions: Our method based on photometric redshifts allows to extend structure detection and density estimates up to the limits of photometric surveys, i.e.considerably deeper than spectroscopic surveys. Since X-ray cluster detection at high redshift is presently limited to massive relaxed structures, galaxy volume density based on photometric redshift appears as a valuable tool in the study of galaxy evolution.

Detection of HNC and tentative detection of CN at z = 3.9

Molecular line emission from high-redshift galaxies holds great promise for the study of galaxy formation and evolution. The weak signals can only be detected with the largest mm-wave telescopes, such as the IRAM interferometer. We report the detection of the J = 5-4 line of HNC and the tentative detection of the N= 4-3 line of CN in the quasar APM08279+5255 at z=3.9. These are the 4th and 5th molecular species detected at such a high redshift. The derived HNC and CN line intensities are 0.6 and 0.4 times that of HCN J= 5-4. If HNC and HCN are co-spatial and if their J= 5-4 lines are collisionally excited, the [HNC]/[HCN] abundance ratio must be equal to 0.6 within a factor of 2, similar to its value in the cold Galactic clouds and much larger than in the hot molecular gas associated with Galactic HII regions. It is possible, however, that fluorescent infrared radiation plays an important role in the excitation of HNC and HCN.

A multi-wavelength study of the IRAS Deep Survey galaxy sample

Context. The luminosity function (LF) is a basic tool in the study of galaxy evolution since it constrains galaxy formation models. The earliest LF estimates in the IR and far-IR spectral ranges seem to suggest strong evolution. Deeper samples are needed to confirm these predictions. We have a useful IR data set, which provides a direct link between IRAS and ISO surveys, and the forthcoming deeper Spitzer Space Telescope and Akari cosmological surveys, to address this issue. Aims. This data set allows us to derive the 60 μ m local LF to sensitivity levels 10 times deeper than before, to investigate evolutionary effects up to a redshift of 0.37, and, using the 60/15 μ m bi-variate method, to analyze the poorly known 15 μ m local LF of galaxies. Methods. We exploited our ISOCAM observations of the IRAS Deep Survey (IDS) fields, to correct the $60~\mu$m fluxes for confusion effects and observational biases. We find indications of a significant incompleteness of the IDS sample, still one of the deepest far-IR selected galaxy samples, below $\simeq$$80~$mJy. We have reliable identifications and spectroscopic redshifts for 100% of a complete subsample comprising 56 sources with $S(60~\mu {\rm m})> 80$ mJy. Results. With our spectroscopic coverage we construct the 60 μ m LF for a sample complete down to 80 mJy. This LF extends over three orders of magnitude in luminosity, from 9 up to more than 12 in $\log(L_{60}/L_{\odot})$. Despite the fact that the redshift range of our sample exceeds $z=0.3$, the $V/V_{\rm max}$ test gives $\langle V/V_{\rm max} \rangle$ = 0.51 ± 0.06, consistent with a uniform distribution of sources. A more direct test, whereby the LF was measured in each of four different redshift intervals, does not point out any signature of evolution. On the other hand, the rest-frame 15 μ m local LF we derive, extends up to $\log(L_{15}/L_{\odot})=12$ and predicts 10 times more sources at $\log(L_{15}/L_{\odot})=11$ than before.

Galaxy morphology and evolution from SWAN adaptive optics imaging

We present the results from adaptive optics (AO) assisted imaging in the Ks band of an area of 15 arcmin^2 for SWAN (Survey of a Wide Area with NACO). We derive the high resolution near-IR morphology of ~400 galaxies up to Ks~23.5 in the first 21 SWAN fields around bright guide stars, carefully taking into account the survey selection effects and using an accurate treatment of the anisoplanatic AO PSF. The detected galaxies are sorted into two morphological classes according to their Sersic index. The extracted morphological properties and number counts of the galaxies are compared with the predictions of different galaxy formation and evolution models, both for the whole galaxy population and separately for late-type and early-type galaxies. This is one of the first times such a comparison has been done in the near-IR, as AO observations and accurate PSF modeling are needed to obtain reliable morphological classification of faint field galaxies at these wavelengths. For early-type galaxies we find that a pure luminosity evolution model, without evidence for relevant number and size evolution, better reproduces the observed properties of our Ks-selected sample than current semi-analytic models based on the hierarchical picture of galaxy formation. In particular, we find that the observed flattening of elliptical galaxy counts at Ks~20 is quantitatively in good agreement with the prediction of the pure luminosity evolution model that was calculated prior to the observation. For late-type galaxies, while both models are able to reproduce the number counts, we find some hints of a possible size growth. These results demonstrate the unique power of AO observations to derive high resolution details of faint galaxies' morphology in the near-IR and drive studies of galaxy evolution.

The 2dF-SDSS LRG and QSO (2SLAQ) Luminous Red Galaxy Survey

We present a spectroscopic survey of almost 15 000 candidate intermediate-redshift luminous red galaxies (LRGs) brighter than i = 19.8, observed with 2dF on the Anglo-Australian Telescope. The targets were selected photometrically from the Sloan Digital Sky Survey (SDSS) and lie along two narrow equatorial strips covering 180 deg 2 . Reliable redshifts were obtained for 92 per cent of the targets and the selection is very efficient: over 90 per cent have 0.45 < z < 0.8. More than 80 per cent of the ∼11 000 red galaxies have pure absorption-line spectra consistent with a passively evolving old stellar population. The redshift, photometric and spatial distributions of the LRGs are described. The 2SLAQ data will be released publicly from mid-2006, providing a powerful resource for observational cosmology and the study of galaxy evolution.

SFR Relation with Galaxy Environment and Colour at z between 0.03 and 0.1

This work is a preliminary result of our attempt to examine the use of SFR in the study of galaxy evolution. For this purpose we use the Sloan Digital Sky Survey Data Release 2 (SDSS DR2) Abazajian et al. (2004) and the SFR Catalogue generated from this data set by Brinchmann et al. (2004) and Kaufmann et al. (2003). Following Kewley et al. (2001) we use the Diagnostic Diagram, log ([OIII]/Hβ) vs log ([NII]/Hα), to separate the star forming galaxies from other emission lines sources such as AGN. Choosing only those with S/N &gt; 3 out of the Brinchmann et al. (2004) catalogue, we arrive at about 200 thousand galaxies as our starting SFR subsample. With 0.05 &lt; z &lt; 0.22 and limit at r = 17.77, the subsample can be used to reconstruct the properties of a volume limited sample of galaxies with M* = 6 1010Modot. We benefit from the fact that Brinchmann et al. (2004) SFR Catalogue has already been aperture-corrected using the likelihood distribution P(SFR/Li/colour) scheme. For the environment, we use the data generated by Kaufmann et al. (2003), and arrive at about 40 thousand target galaxies. In this work the environment is characterised by the number (N=0-30) of neighbouring galaxies within a projected radius of 2 Mpc and velocity di.erence of 500km/s from each target galaxy, and the magnitude limit is 14.5 &lt; r &lt; 17.77.

The Chemical Enrichment and Mass Assembly Histories of SDSS Galaxies

AbstractWe explore the mass-assembly and chemical enrichment histories of star forming galaxies by applying a population synthesis method to a sample of nearly 70k galaxies culled from over 500k galaxies from the Sloan Digital Sky Survey Data Release 5. Our method decomposes the entire observed spectrum in terms of a sum of simple stellar populations spanning a wide range of ages and metallicities, thus allowing the reconstruction of galaxy histories. A comparative study of galaxy evolution is presented, where galaxies are grouped onto bins of nebular abundances or mass. We find that galaxies whose warm interstellar medium is poor in heavy elements are slow in forming stars. Their stellar metallicities also rise slowly with time, reaching their current values (Z⋆ ~ 1/4Z⊙) in the last ~100 Myr of evolution. Systems with metal rich nebulae, on the other hand, assembled most of their mass and completed their chemical evolution long ago, reaching Z⋆ ~ Z⊙ already at lookback times of a few Gyr. These same trends, which are ultimately a consequence of galaxy downsizing, appear when galaxies are grouped according to their stellar mass. The reconstruction of galaxy histories to this level of detail out of integrated spectra offers promising prospects in the field of galaxy evolution theories.

Poor Groups Around Strong Gravitational Lenses

AbstractPoor groups are common and interactive environments for galaxies, and thus are important laboratories for studying galaxy evolution. Unfortunately, little is known about groups at z ≥ 0.1, because of the difficulty in identifying them in the first place. Here we present results from our ongoing survey of the environments of strong gravitational lenses, in which we have so far discovered six distant (z ≥ 0.5) groups of galaxies. As in the local Universe, the highest velocity dispersion groups contain a brightest member spatially coincident with the group centroid, whereas lower-dispersion groups tend to have an offset brightest group galaxy. This suggests that higher-dispersion groups are more dynamically relaxed than lower-dispersion groups and that at least some evolved groups exist by z ~ 0.5. We also compare the galaxy and hot gas kinematics with those of similarly distant clusters and of nearby groups.

The FLAMINGOS Extragalactic Survey

Using the Florida Multi-object Imaging Near-IR grism Observational Spectrometer (FLAMINGOS), we have conducted the FLAMINGOS Extragalactic Survey (FLAMEX), a deep imaging survey covering 7.1 square degrees within the 18.6 sq. deg NOAO Deep Wide-Field Survey (NDWFS) regions. FLAMEX is the first deep, wide-area near-infrared survey to image in both the J and Ks filters, and is larger than any previous NIR surveys of comparable depth. The intent of FLAMEX is to facilitate the study of galaxy and galaxy cluster evolution at 1 1 galaxy clusters detected using the joint FLAMEX, NDWFS, and Spitzer IRAC Shallow Survey data sets.

Strong Emission-Line Galaxies at Low Redshifts in the Field around the Quasar SDSSp J104433.04−012502.2

Abstract We discuss the observational properties of strong emission-line galaxies at low redshifts found by our deep imaging survey for high-redshift Ly$\alpha$ emitters. In our survey, we used a narrow-band filter, NB816 ($\lambda_{\mathrm{center}} = 8150 \,{Å}$ with $\mbox{FWHM} = 120 \,\mbox{Å}$ FWHM$= 120 \,{Å}$), and an intermediate-band filter, IA827 ($\lambda_{\mathrm{center}} = 8270 \,{Å}$ with $\mbox{FWHM} = 340 \,\mbox{Å}$ FWHM$= 340 \,{Å}$). In this survey, 62 NB816-excess ($\gt 0.9 \,\mathrm{mag} \gt 0.9 \,\mathrm{mag}$) and 21 IA827-excess ($\gt 0.8 \,\mathrm{mag} \gt 0.8 \,\mathrm{mag}$) objects were found. Among them, we found 20 NB816-excess and 4 IA827-excess Ly$\alpha$ emitter candidates. Therefore, it turns out that 42 NB816-excess and 17 IA827-excess objects are strong emission-line objects at lower redshifts. Since 4 objects in the two low-$z$ samples are common, the total number of strong low-$z$ emitters is 55. Applying our photometric redshift technique, we identified 7 $\mathrm{H}\alpha$ emitters at $z \approx 0.24$, 20 $\mathrm{H}\beta$–[O III] ones at $z \approx 0.65$, and 11 [O II] ones at $z \approx 1.19$. However, we could not determine reliable photometric redshifts of the remaining 17 emitters. The distributions of their rest frame equivalent widths are consistently understood based on recent studies of galaxy evolution from $z \sim 1$ to $z \sim 0$.

Synergies between ELTs and the SKA

Over the coming two decades astronomers will plan, construct and exploit extremely large telescopes operating at both optical (ELTs) and radio (SKA) wavelengths. In studies of galaxy evolution and cosmology the combination of the two types of facility are likely to be extremely powerful. In this paper I will review the key questions that the ELT/SKA combination seem set to solve, focussing on the unique advantages afforded by optical and radio observations against the backdrop of the other theoretical and observational information to be available by 2020.

A most useful manifestation of relativity: gravitational lenses

Gravitational lenses are scarce but extraordinary phenomena that yield a very high rate of return on observational investment. Given their scarcity, it is very impressive that since their discovery in the extragalactic realm in 1979, they have had such an enormous impact on our knowledge of the universe. Gravitational lensing is a manifestation of general relativity that has contributed to a great variety of astrophysical and cosmological studies. In the weak-field limit, lensing studies are based on well-established physics and thus offer a direct approach to study many of the currently pressing problems of astrophysics. Examples of these are the significance of dark matter and the age and size of the universe. I present a brief history of gravitational lensing and describe recent developments in fields such as searches for dark matter and studies of galaxy evolution and cosmology. The approach is non-specialized and emphasizes observational results, to reach the widest possible audience.

Molecular Gas at High Redshift

▪ Abstract The Early Universe Molecular Emission Line Galaxies (EMGs) are a population of galaxies with only 36 examples that hold great promise for the study of galaxy formation and evolution at high redshift. The classification, luminosity of molecular line emission, molecular mass, far-infrared (FIR) luminosity, star formation efficiency, morphology, and dynamical mass of the currently known sample are presented and discussed. The star formation rates derived from the FIR luminosity range from about 300 to 5000 M⊙ year −1 and the molecular mass from 4 × 109 to 1 × 1011 M⊙. At the lower end, these star formation rates, gas masses, and diameters are similar to those of local ultraluminous infrared galaxies and represent starbursts in centrally concentrated disks, sometimes, but not always, associated with active galactic nuclei. The evidence for large (&gt;5 kpc) molecular disks is limited. Morphology and several high angular resolution images suggest that some EMGs are mergers with a massive molecular interstellar medium in both components. A critical question is whether the EMGs, in particular those at the higher end of the gas mass and luminosity distribution, represent the formation of massive, giant elliptical galaxies in the early Universe. The sample size is expected to grow explosively in the era of the Atacama Large Millimeter Array (ALMA).

Accounting for the anisoplanatic point spread function in deep wide-field adaptive optics images

In this paper we present the approach we have used to determine and account for the anisoplanatic point spread function (PSF) in deep adaptive optics (AO) images for the Survey of a Wide Area with NACO (SWAN) at the ESO VLT. The survey comprises adaptive optics observations in the Ks band totaling ~, assembled from 42 discrete fields centered on different bright stars suitable for AO guiding. We develop a parametric model of the PSF variations across the field of view in order to build an accurate model PSF for every galaxy detected in each of the fields. We show that this approach is particularly convenient, as it uses only easily available data and makes no uncertain assumptions about the stability of the isoplanatic angle during any given night. The model was tested using simulated galaxy profiles to check its performance in terms of recovering the correct morphological parameters; we find that the results are reliable up to () in a typical SWAN field. Finally, the model obtained was used to derive the first results from five SWAN fields, and to obtain the AO morphology of 55 galaxies brighter than . These preliminary results demonstrate the unique power of AO observations to derive the details of faint galaxy morphologies and to study galaxy evolution.

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.