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Register a new userThe dearth of difference between central and satellite galaxies II. Comparison of observations with L-GALAXIES and EAGLE in star formation quenching
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As we demonstrated in Paper I, the quenched fractions of central and satellite galaxies as function of halo mass are extremely similar, as long as one controls for stellar mass. The same holds for the quenched fractions as a function of central velocity dispersion, which is tightly correlated with black hole mass, as long as one controls for both stellar and halo mass. Here we use mock galaxy catalogs constructed from the latest semi-analytic model, L-GALAXIES, and the state-of-the-art hydrodynamical simulation, EAGLE, to investigate whether these models can reproduce the trends seen in the data. We also check how the group finder used to identify centrals and satellites impacts our results. We find that L-GALAXIES fails to reproduce the trends. The predicted quenched fraction of central galaxies increases sharply with halo mass around $10^{12.5}h^{-1}M_{odot}$ and with black hole mass around $sim10^{6.5}M_{odot}$, while the predicted quenched fraction of satellites increases with both halo and black hole masses gradually. In contrast, centrals and satellites in EAGLE follow almost the same trend as seen in the data. We discuss the implications of our results for how feedback processes regulate galaxy quenching.
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We investigate the quenching properties of central and satellite galaxies, utilizing the halo masses and central-satellite identifications from the SDSS galaxy group catalog of Yang et al. We find that the quenched fractions of centrals and satellites of similar stellar masses have similar dependence on host halo mass. The similarity of the two populations is also found in terms of specific star formation rate and 4000 AA break. The quenched fractions of centrals and satellites of similar masses show similar dependencies on bulge-to-total light ratio, central velocity dispersion and halo-centric distance in halos of given halo masses. The prevalence of optical/radio-loud AGNs is found to be similar for centrals and satellites at given stellar masses. All these findings strongly suggest that centrals and satellites of similar masses experience similar quenching processes in their host halos. We discuss implications of our results for the understanding of galaxy quenching.
As demonstrated in Paper I, the quenching properties of central and satellite galaxies are quite similar as long as both stellar mass and halo mass are controlled. Here we extend the analysis to the size and bulge-to-total light ratio (B/T) of galaxies. In general central galaxies have size-stellar mass and B/T-stellar mass relations different from satellites. However, the differences are eliminated when halo mass is controlled. We also study the dependence of size and B/T on halo-centric distance and find a transitional stellar mass (M$_{*,t}$) at given halo mass (M$_h$), which is about one fifth of the mass of the central galaxies in halos of mass M$_h$. The transitional stellar masses for size, B/T and quenched fraction are similar over the whole halo mass range, suggesting a connection between the quenching of star formation and the structural evolution of galaxies. Our analysis further suggests that the classification based on the transitional stellar mass is more fundamental than the central-satellite dichotomy, and provide a more reliable way to understand the environmental effects on galaxy properties. We compare the observational results with the hydro-dynamical simulation, EAGLE and the semi-analytic model, L-GALAXIES. The EAGLE simulation successfully reproduces the similarities of size for centrals and satellites and even M$_{*,t}$, while L-GALAXIES fails to recover the observational results.
We quantitatively investigate the dependence of central galaxy HI mass ($M_{rm HI}$) on the stellar mass ($M_ast$), halo mass ($M_{rm h}$), star formation rate (SFR), and central stellar surface density within 1 kpc ($Sigma_1$), taking advantage of the HI spectra stacking technique using both the Arecibo Fast Legacy ALFA Survey and the Sloan Digital Sky Survey. We find that the shapes of $M_{rm HI}$-$M_{rm h}$ and $M_{rm HI}$-$M_ast$ relations are remarkably similar for both star-forming and quenched galaxies, with massive quenched galaxies having constantly lower HI masses of around 0.6 dex. This similarity strongly suggests that neither halo mass nor stellar mass is the direct cause of quenching, but rather the depletion of HI reservoir. While the HI reservoir for low-mass galaxies of $M_ast<10^{10.5}M_odot$ strongly increases with $M_{rm h}$, more massive galaxies show no significant dependence of $M_{rm HI}$ on $M_{rm h}$, indicating the effect of halo to determine the smooth cold gas accretion. We find that the star formation and quenching of central galaxies are directly regulated by the available HI reservoir, with an average relation of ${rm SFR}propto M_{rm HI}^{2.75}/M_ast^{0.40}$, implying a quasi-steady state of star formation. We further confirm that galaxies are depleted of their HI reservoir once they drop off the star-formation main sequence and there is a very tight and consistent correlation between $M_{rm HI}$ and $Sigma_1$ in this phase, with $M_{rm HI}proptoSigma_1^{-2}$. This result is in consistent with the compaction-triggered quenching scenario, with galaxies going through three evolutionary phases of cold gas accretion, compaction and post-compaction, and quenching.
We use the eagle simulations to study the connection between the quenching timescale, $tau_{rm Q}$, and the physical mechanisms that transform star-forming galaxies into passive galaxies. By quantifying $tau_{rm Q}$ in two complementary ways - as the time over which (i) galaxies traverse the green valley on the colour-mass diagram, or (ii) leave the main sequence of star formation and subsequently arrive on the passive cloud in specific star formation rate (SSFR)-mass space - we find that the $tau_{rm Q}$ distribution of high-mass centrals, low-mass centrals and satellites are divergent. In the low stellar mass regime where $M_{star}<10^{9.6}M_{odot}$, centrals exhibit systematically longer quenching timescales than satellites ($approx 4$~Gyr compared to $approx 2$~Gyr). Satellites with low stellar mass relative to their halo mass cause this disparity, with ram pressure stripping quenching these galaxies rapidly. Low mass centrals are quenched as a result of stellar feedback, associated with long $tau_{rm Q}gtrsim 3$~Gyr. At intermediate stellar masses where $10^{9.7},rm M_{odot}<M_{star}<10^{10.3},rm M_{odot}$, $tau_{rm Q}$ are the longest for both centrals and satellites, particularly for galaxies with higher gas fractions. At $M_{star}gtrsim 10^{10.3},rm M_{odot}$, galaxy merger counts and black hole activity increase steeply for all galaxies. Quenching timescales for centrals and satellites decrease with stellar mass in this regime to $tau_{rm Q}lesssim2$~Gyr. In anticipation of new intermediate redshift observational galaxy surveys, we analyse the passive and star-forming fractions of galaxies across redshift, and find that the $tau_{rm Q}$ peak at intermediate stellar masses is responsible for a peak (inflection point) in the fraction of green valley central (satellite) galaxies at $zapprox 0.5-0.7$.
We combine orbital information from N-body simulations with an analytic model for star formation quenching and SDSS observations to infer the differential effect of the group/cluster environment on star formation in satellite galaxies. We also consider a model for gas stripping, using the same input supplemented with HI fluxes from the ALFALFA survey. The models are motivated by and tested on the Hydrangea cosmological hydrodynamical simulation suite. We recover the characteristic times when satellite galaxies are stripped and quenched. Stripping in massive ($M_mathrm{ vir}sim 10^{14.5},mathrm{M}_odot$) clusters typically occurs at or just before the first pericentric passage. Lower mass ($sim10^{13.5},mathrm{M}_odot$) groups strip their satellites on a significantly longer (by $sim3,mathrm{Gyr}$) timescale. Quenching occurs later: Balmer emission lines typically fade $sim3.5,mathrm{Gyr}$ ($5.5,mathrm{Gyr}$) after first pericentre in clusters (groups), followed a few hundred $mathrm{Myr}$ later by reddenning in $(g-r)$ colour. These `delay timescales are remarkably constant across the entire satellite stellar mass range probed ($sim10^{9.5}-10^{11},mathrm{M}_odot$), a feature closely tied to our treatment of `group pre-processing. The lowest mass groups in our sample ($sim10^{12.5},mathrm{M}_odot$) strip and quench their satellites extremely inefficiently: typical timescales may approach the age of the Universe. Our measurements are qualitatively consistent with the `delayed-then-rapid quenching scenario advocated for by several other studies, but we find significantly longer delay times. Our combination of a homogeneous analysis and input catalogues yields new insight into the sequence of events leading to quenching across wide intervals in host and satellite mass.
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