The Baryon Content of Extremely Low Mass Dwarf Galaxies

We investigate the gas content and baryonic Tully-Fisher relationship for extremely low luminosity dwarf galaxies in the absolute magnitude range -13.5 > Mr > -16. The sample is selected from the Sloan Digital Sky Survey and consists of 101 galaxies for which we have obtained follow-up HI observations using the Arecibo Observatory and Green Bank Telescope. This represents the largest homogeneous sample of dwarfs at low luminosities with well-measured HI and optical properties. The sample spans a range of environments, from dense groups to truly isolated galaxies. The average neutral gas fraction is f_gas=0.6, significantly exceeding that of typical gas-rich galaxies at higher luminosities. Dwarf galaxies are therefore less efficient at turning gas into stars over their lifetimes. The strong environmental dependence of the gas fraction distribution demonstrates that while internal processes can reduce the gas fractions to roughly f_gas=0.4, external processes are required to fully remove gas from a dwarf galaxy. The average rotational velocity of our sample is vrot=50 km/s. Including more massive galaxies from the literature, we fit a baryonic Tully-Fisher slope of M_baryon \propto vrot^(3.70+/- 0.15). This slope compares well with CDM models that assume an equal baryon to dark matter ratio at all masses. While gas stripping or other processes may modify the baryon to dark matter ratio for dwarfs in the densest environments, the majority of dwarf galaxies in our sample have not preferentially lost significant baryonic mass relative to more massive galaxies.Comment: 33 pages, 8 figures. Accepted to ApJ. Data available at http://www.ociw.edu/~mgeha/researc

What triggers galaxy transformations? The environments of post-starburst galaxies

(abridged) There are good observational reasons to believe that the progenitors of red galaxies have undergone starbursts, followed by a post-starburst phase. We investigate the environments of post-starburst galaxies by measuring \textsl{(1)} number densities in $8 h^{-1} \mathrm{Mpc}$ radius comoving spheres, \textsl{(2)} transverse distances to nearest Virgo-like galaxy clusters, and \textsl{(3)} transverse distances to nearest luminous-galaxy neighbors. We compare the post-starburst galaxies to currently star-forming galaxies identified solely by A-star excess or \Halpha emission. We find that post-starburst galaxies are in the same kinds of environments as star-forming galaxies; this is our ``null hypothesis''. More importantly, we find that at each value of the A-star excess, the star-forming and post-starburst galaxies lie in very similar distributions of environment. The only deviations from our null hypothesis are barely significant: a slight deficit of post-starburst galaxies (relative to the star-forming population) in very low-density regions, a small excess inside the virial radii of clusters, and a slight excess with nearby neighbors. None of these effects is strong enough to make the post-starburst galaxies a high-density phenomenon, or to argue that the starburst events are primarily triggered by external tidal impulses (e.g., from close passages of massive galaxies). The small excess inside cluster virial radii suggests that some post-starbursts are triggered by interactions with the intracluster medium, but this represents a very small fraction of all post-starburst galaxies.Comment: ApJ in pres

Cross-correlation Weak Lensing of SDSS Galaxy Clusters III: Mass-to-light Ratios

We present measurements of the excess mass-to-light ratio measured aroundMaxBCG galaxy clusters observed in the SDSS. This red sequence cluster sample includes objects from small groups with masses ranging from ~5x10^{12} to ~10^{15} M_{sun}/h. Using cross-correlation weak lensing, we measure the excess mass density profile above the universal mean \Delta \rho(r) = \rho(r) - \bar{\rho} for clusters in bins of richness and optical luminosity. We also measure the excess luminosity density \Delta l(r) = l(r) - \bar{l} measured in the z=0.25 i-band. For both mass and light, we de-project the profiles to produce 3D mass and light profiles over scales from 25 kpc/ to 22 Mpc/h. From these profiles we calculate the cumulative excess mass M(r) and excess light L(r) as a function of separation from the BCG. On small scales, where \rho(r) >> \bar{\rho}, the integrated mass-to-light profile may be interpreted as the cluster mass-to-light ratio. We find the M/L_{200}, the mass-to-light ratio within r_{200}, scales with cluster mass as a power law with index 0.33+/-0.02. On large scales, where \rho(r) ~ \bar{\rho}, the M/L approaches an asymptotic value independent of cluster richness. For small groups, the mean M/L_{200} is much smaller than the asymptotic value, while for large clusters it is consistent with the asymptotic value. This asymptotic value should be proportional to the mean mass-to-light ratio of the universe . We find /b^2_{ml} = 362+/-54 h (statistical). There is additional uncertainty in the overall calibration at the ~10% level. The parameter b_{ml} is primarily a function of the bias of the L <~ L_* galaxies used as light tracers, and should be of order unity. Multiplying by the luminosity density in the same bandpass we find \Omega_m/b^2_{ml} = 0.02+/-0.03, independent of the Hubble parameter.Comment: Third paper in a series; v2.0 incorporates ApJ referee's suggestion

A Search for the Most Massive Galaxies. II. Structure, Environment and Formation

We study a sample of 43 early-type galaxies, selected from the SDSS because they appeared to have velocity dispersion > 350 km/s. High-resolution photometry in the SDSS i passband using HRC-ACS on board the HST shows that just less than half of the sample is made up of superpositions of two or three galaxies, so the reported velocity dispersion is incorrect. The other half of the sample is made up of single objects with genuinely large velocity dispersions. None of these objects has sigma larger than 426 +- 30 km/s. These objects define rather different relations than the bulk of the early-type galaxy population: for their luminosities, they are the smallest, most massive and densest galaxies in the Universe. Although the slopes of the scaling relations they define are rather different from those of the bulk of the population, they lie approximately parallel to those of the bulk "at fixed sigma". These objects appear to be of two distinct types: the less luminous (M_r>-23) objects are rather flattened and extremely dense for their luminosities -- their properties suggest some amount of rotational support and merger histories with abnormally large amounts of gaseous dissipation. The more luminous objects (M_r<-23) tend to be round and to lie in or at the centers of clusters. Their properties are consistent with the hypothesis that they are BCGs. Models in which BCGs form from predominantly radial mergers having little angular momentum predict that they should be prolate. If viewed along the major axis, such objects would appear to have abnormally large sigma for their sizes, and to be abnormally round for their luminosities. This is true of the objects in our sample once we account for the fact that the most luminous galaxies (M_r<-23.5), and BCGs, become slightly less round with increasing luminosity.Comment: 21 pages, 19 figures, accepted for publication in MNRA

The luminosity -- halo-mass relation for brightest cluster galaxies

We examine the central-galaxy luminosity -- host-halo mass relation for 54 Brightest Group Galaxies (BGGs) and 92 Brightest Cluster Galaxies (BCGs) at z<0.1 and present the first measurement of this relation for a sample of known BCGs at 0.1<z<0.8 (average z~0.3). At z<0.1 we find L_K \propto M_{200}^{0.24\pm0.08} for the BCGs and the early-type BGGs in groups with extended X-ray emission and L_K \propto M_{200}^{0.11\pm0.10} for the BCGs alone. At 0.1<z<0.8 we find L_K \propto M_{200}^{0.28\pm0.11}. We conclude that there is no evidence for evolution in this relationship between z<0.1 and z<0.8: BCG growth appears to still be limited by the timescale for dynamical friction at these earlier times, not proceeding according to the predictions of current semi-analytic models.Comment: Accepted for publication in MNRA

Improved constraints on the expansion rate of the Universe up to z~1.1 from the spectroscopic evolution of cosmic chronometers

We present new improved constraints on the Hubble parameter H(z) in the redshift range 0.15 < z < 1.1, obtained from the differential spectroscopic evolution of early-type galaxies as a function of redshift. We extract a large sample of early-type galaxies (\sim11000) from several spectroscopic surveys, spanning almost 8 billion years of cosmic lookback time (0.15 < z < 1.42). We select the most massive, red elliptical galaxies, passively evolving and without signature of ongoing star formation. Those galaxies can be used as standard cosmic chronometers, as firstly proposed by Jimenez & Loeb (2002), whose differential age evolution as a function of cosmic time directly probes H(z). We analyze the 4000 {\AA} break (D4000) as a function of redshift, use stellar population synthesis models to theoretically calibrate the dependence of the differential age evolution on the differential D4000, and estimate the Hubble parameter taking into account both statistical and systematical errors. We provide 8 new measurements of H(z) (see Tab. 4), and determine its change in H(z) to a precision of 5-12% mapping homogeneously the redshift range up to z \sim 1.1; for the first time, we place a constraint on H(z) at z \neq 0 with a precision comparable with the one achieved for the Hubble constant (about 5-6% at z \sim 0.2), and covered a redshift range (0.5 < z < 0.8) which is crucial to distinguish many different quintessence cosmologies. These measurements have been tested to best match a \Lambda CDM model, clearly providing a statistically robust indication that the Universe is undergoing an accelerated expansion. This method shows the potentiality to open a new avenue in constrain a variety of alternative cosmologies, especially when future surveys (e.g. Euclid) will open the possibility to extend it up to z \sim 2.Comment: 34 pages, 15 figures, 6 tables, published in JCAP. It is a companion to Moresco et al. (2012b, http://arxiv.org/abs/1201.6658) and Jimenez et al. (2012, http://arxiv.org/abs/1201.3608). The H(z) data can be downloaded at http://www.physics-astronomy.unibo.it/en/research/areas/astrophysics/cosmology-with-cosmic-chronometer

Building galaxies by accretion and in-situ star formation

We examine galaxy formation in a cosmological AMR simulation, which includes two high resolution boxes, one centered on a 3 \times 10^14 M\odot cluster, and one centered on a void. We examine the evolution of 611 massive (M\ast > 10^10M\odot) galaxies. We find that the fraction of the final stellar mass which is accreted from other galaxies is between 15 and 40% and increases with stellar mass. The accreted fraction does not depend strongly on environment at a given stellar mass, but the galaxies in groups and cluster environments are older and underwent mergers earlier than galaxies in lower density environments. On average, the accreted stars are ~2.5 Gyrs older, and ~0.15 dex more metal poor than the stars formed in-situ. Accreted stellar material typically lies on the outskirts of galaxies; the average half-light radius of the accreted stars is 2.6 times larger than that of the in-situ stars. This leads to radial gradients in age and metallicity for massive galaxies, in qualitative agreement with observations. Massive galaxies grow by mergers at a rate of approximately 2.6% per Gyr. These mergers have a median (mass-weighted) mass ratio less than 0.26 \pm 0.21, with an absolute lower limit of 0.20, for galaxies with M\ast ~ 10^12 M\odot. This suggests that major mergers do not dominate in the accretion history of massive galaxies. All of these results agree qualitatively with results from SPH simulations by Oser et al. (2010, 2012).Comment: 18 pages, 12 figures, submitted to MNRA

CANDELS Observations of the Structural Properties and Evolution of Galaxies in a Cluster at z=1.62

We discuss the structural and morphological properties of galaxies in a z=1.62 proto-cluster using near-IR imaging data from Hubble Space Telescope Wide Field Camera 3 data of the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS). The cluster galaxies exhibit a clear color-morphology relation: galaxies with colors of quiescent stellar populations generally have morphologies consistent with spheroids, and galaxies with colors consistent with ongoing star formation have disk-like and irregular morphologies. The size distribution of the quiescent cluster galaxies shows a deficit of compact (< 1kpc), massive galaxies compared to CANDELS field galaxies at z=1.6. As a result the cluster quiescent galaxies have larger average effective sizes compared to field galaxies at fixed mass at greater than 90% significance. Combined with data from the literature, the size evolution of quiescent cluster galaxies is relatively slow from z~1.6 to the present, growing as (1+z)^(-0.6+/-0.1). If this result is generalizable, then it implies that physical processes associated with the denser cluster region seems to have caused accelerated size growth in quiescent galaxies prior to z=1.6 and slower subsequent growth at z<1.6 compared to galaxies in the lower density field. The quiescent cluster galaxies at z=1.6 have higher ellipticities compared to lower redshift samples at fixed mass, and their surface-brightness profiles suggest that they contain extended stellar disks. We argue the cluster galaxies require dissipationless (i.e., gas-poor or "dry") mergers to reorganize the disk material and to match the relations for ellipticity, stellar mass, size, and color of early-type galaxies in z<1 clusters.Comment: Accepted for publication in ApJ. 14 pages in emulateapj format. Replacement includes improvements from referee report, and updates and additions to reference

Nutrition and lung cancer: a case control study in Iran

Background: Despite many prospective and retrospective studies about the association of dietary habit and lung cancer, the topic still remains controversial. So, this study aims to investigate the association of lung cancer with dietary factors. Method: In this study 242 lung cancer patients and their 484 matched controls on age, sex, and place of residence were enrolled between October 2002 to 2005. Trained physicians interviewed all participants with standardized questionnaires. The middle and upper third consumer groups were compared to the lower third according to the distribution in controls unless the linear trend was significant across exposure groups. Result: Conditional logistic regression was used to evaluate the association with lung cancer. In a multivariate analysis fruit (Ptrend < 0.0001), vegetable (P = 0.001) and sunflower oil (P = 0.006) remained as protective factors and rice (P = 0.008), bread (Ptrend = 0.04), liver (P = 0.004), butter (Ptrend = 0.04), white cheese (Ptrend < 0.0001), beef (Ptrend = 0.005), vegetable ghee (P < 0.0001) and, animal ghee (P = 0.015) remained as risk factors of lung cancer. Generally, we found positive trend between consumption of beef (P = 0.002), bread (P < 0.0001), and dairy products (P < 0.0001) with lung cancer. In contrast, only fruits were inversely related to lung cancer (P < 0.0001). Conclusion: It seems that vegetables, fruits, and sunflower oil could be protective factors and bread, rice, beef, liver, dairy products, vegetable ghee, and animal ghee found to be possible risk factors for the development of lung cancer in Iran

Evolution of the Far-Infrared-Radio Correlation and Infrared SEDs of Massive Galaxies over z = 0 - 2

We investigate the far-infrared-radio correlation (FRC) of stellar-mass-selected galaxies in the Extended Chandra Deep Field South using far-infrared imaging from Spitzer and radio imaging from the Very Large Array and Giant Metre-Wave Radio Telescope. We stack in redshift bins to probe galaxies below the noise and confusion limits. Radio fluxes are K-corrected using observed flux ratios, leading to tentative evidence for an evolution in spectral index. We compare spectral energy distribution (SED) templates of local galaxies for K-correcting FIR fluxes, and show that the data are best fit by a quiescent spiral template (M51) rather than a warm starburst (M82) or ULIRG (Arp220), implying a predominance of cold dust in massive galaxies at high redshift. In contrast we measure total infrared luminosities that are consistent with high star-formation rates. We observe that the FRC index (q) does not evolve significantly over z=0-2 when computed from K-corrected 24 or 160-mum photometry, but that using 70-mum fluxes leads to an apparent decline in q beyond z~1. This suggests some change in the SED at high redshift, either a steepening of the spectrum at rest-frame ~25-35mum or a deficiency at ~70mum leading to a drop in the total infrared/radio ratios. We compare our results to other work in the literature and find synergies with recent findings on the high-redshift FRC, high specific star-formation rates of massive galaxies and the cold dust temperatures in these galaxies.Comment: 21 pages, 13 figures, accepted for publication in MNRA