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Nandan Chengguanzhen, China

Kauffmann G.,Max Planck Institute for Astrophysics | Li C.,Max Planck Institute Partner Group | Zhang W.,CAS National Astronomical Observatories | Weinmann S.,Leiden Observatory
Monthly Notices of the Royal Astronomical Society | Year: 2013

The observed correlation between star formation in central galaxies and in their neighbours (a phenomenon dubbed 'galactic conformity') is in need of a convincing physical explanation. To gain further insight, we use a volume-limited sample of galaxies with redshifts less than 0.03 drawn from the Sloan Digital Sky Survey Data Release 7 to investigate the scale dependence of the effect and how it changes as a function of the mass of the central galaxy. Conformity extends over a central galaxy stellar mass range spanning two orders of magnitude. The scale dependence and the precise nature of the effect depend on the mass of the central. In central galaxies with masses less than 1010M⊙, conformity extends out to scales in excess of 4 Mpc, well beyond the virial radii of their dark matter haloes. For low-mass central galaxies, conformity with neighbours on very large scales is only seen when they have lowstar formation rate or gas content. In contrast, at high stellar masses, conformity with neighbours applies in the gas-rich regime and is clearly confined to scales comparable to the virial radius of the dark matter halo of the central galaxy. Our analysis of a mock catalogue from the Guo et al. semianalytic models shows that conformity-like effects arise because gas-poor satellite galaxies are sometimes misclassified as centrals. However, the effects in the models are much weaker than observed. Misclassification only influences the low-end tail of the SFR/M* distribution of neighbouring galaxies at large distances from the primary. The median and the upper percentiles of the SFR/M* distribution remain almost unchanged, which is in contradiction with the data. We speculate that the conformity between low-mass, gas-poor central galaxies and their distant neighbours may be a signature of 'pre-heating' of the intergalactic gas at an earlier epoch. The smaller scale conformity between high-mass, gas-rich central galaxies and their close neighbours may be a signature of ongoing gas accretion on to central galaxies in a minority of massive dark matter haloes. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

Li C.,Max Planck Institute Partner Group
Proceedings of the International Astronomical Union | Year: 2012

We use data from the Sloan Digital Sky Survey (SDSS) and the DEEP2 survey to characterize the distribution of stellar mass and light of galaxies in the low-redshift and z = 1 Universe. We investigate the clustering bias of stellar mass and light by comparing these to projected autocorrelations of dark matter estimated from the Millennium Simulations (MS). All of the autocorrelation and bias functions show systematic trends with spatial scale and waveband, which are impressively similar at the two redshifts. This shows that the well-established environmental dependence of stellar populations in the local Universe is already in place at z = 1. The recent MS-based galaxy formation simulation of Guo et al. (2011) reproduces the scale-dependent clustering of luminosity to an accuracy better than 30% in all bands and at both redshifts, but substantially overpredicts mass autocorrelations at separations below ∼ 2 Mpc. Further comparison of the shapes of our stellar mass bias functions with those predicted by the model suggests that both the SDSS and DEEP2 data prefer a fluctuation amplitude of σ8 ∼ 0.8 rather than the σ8 = 0.9 assumed by the MS. © 2013 International Astronomical Union. Source

Li C.,Max Planck Institute Partner Group
Proceedings of the International Astronomical Union | Year: 2012

Effects of galaxy environment on its cold gas content are studied in detail using different date sets and statistics. These include measuring the clustering of galaxies as a function of their Hi mass fraction, quantifying the depletion of Hi gas content of cluster galaxies as a function of cluster-centric radius, and comparing the dependence of environmental density on galaxy star formation rate with the dependence on Hi gas mass fraction. Results from these studies are all consistent with a picture in which ram-pressure stripping may play an important role in removing atomic gas from the outer disks of low mass satellite galaxies. © 2013 International Astronomical Union. Source

Fabello S.,Max Planck Institute for Astrophysics | Kauffmann G.,Max Planck Institute for Astrophysics | Catinella B.,Max Planck Institute for Astrophysics | Li C.,Max Planck Institute Partner Group | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2012

It is well known that both the star formation rate and the cold gas content of a galaxy depend on the local density out to distances of a few Mpc. In this paper, we compare the environmental density dependence of the atomic gas mass fractions of nearby galaxies with the density dependence of their central and global specific star formation rates. We stack HI line spectra extracted from the Arecibo Legacy Fast ALFA survey centred on galaxies with ultraviolet imaging from GALEX and optical imaging/spectroscopy from Sloan Digital Sky Survey. We use these stacked spectra to evaluate the mean atomic gas mass fraction of galaxies in bins of stellar mass and local density. For galaxies with stellar masses less than 1010.5M⊙, the decline in mean atomic gas mass fraction with density is stronger than the decline in mean global and central specific star formation rate. The same conclusion does not hold for more massive galaxies. We interpret our results as evidence for ram-pressure stripping of atomic gas from the outer discs of low-mass satellite galaxies. We compare our results with the semi-analytic recipes of Guo et al. implemented on the Millennium II Simulation. These models assume that only the diffuse gas surrounding satellite galaxies is stripped, a process that is often termed 'strangulation'. We show that these models predict relative trends in atomic gas and star formation that are in disagreement with observations. We use mock catalogues generated from the simulation to predict the halo masses of the HI-deficient galaxies in our sample. We conclude that ram-pressure stripping is likely to become effective in dark matter haloes with masses greater than 1013 M⊙. © 2012 The Authors. Source

Saintonge A.,Max Planck Institute for Astrophysics | Saintonge A.,Max Planck Institute for Extraterrestrial Physics | Kauffmann G.,Max Planck Institute for Astrophysics | Kramer C.,Instituto Radioastronomia Milimetrica | And 25 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2011

We are conducting COLD GASS, a legacy survey for molecular gas in nearby galaxies. Using the IRAM 30-m telescope, we measure the CO(1-0) line in a sample of ~350 nearby (Mpc), massive galaxies (log(M*/M⊙) > 10.0). The sample is selected purely according to stellar mass, and therefore provides an unbiased view of molecular gas in these systems. By combining the IRAM data with Sloan Digital Sky Survey (SDSS) photometry and spectroscopy, GALEX imaging and high-quality Arecibo Hi data, we investigate the partition of condensed baryons between stars, atomic gas and molecular gas in 0.1-10L* galaxies. In this paper, we present CO luminosities and molecular hydrogen masses for the first 222 galaxies. The overall CO detection rate is 54 per cent, but our survey also uncovers the existence of sharp thresholds in galaxy structural parameters such as stellar mass surface density and concentration index, below which all galaxies have a measurable cold gas component but above which the detection rate of the CO line drops suddenly. The mean molecular gas fractionof the CO detections is 0.066 ± 0.039, and this fraction does not depend on stellar mass, but is a strong function of (NUV -r) colour. Through stacking, we set a firm upper limit offor red galaxies with NUV -r> 5.0. The average molecular-to-atomic hydrogen ratio in present-day galaxies is 0.3, with significant scatter from one galaxy to the next. The existence of strong detection thresholds in both the Hi and CO lines suggests that 'quenching' processes have occurred in these systems. Intriguingly, atomic gas strongly dominates in the minority of galaxies with significant cold gas that lie above these thresholds. This suggests that some re-accretion of gas may still be possible following the quenching event. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS. Source

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