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-The morphological types of galaxies as a function of their rest-frame V-band absolute magnitude and U − V color over the last half of cosmic history. a) The colors and magnitudes of 1500 morphologically-classified local Universe galaxies from the SDSS. Blue open circles denote morphologically-classified latetype galaxies (cr < 2.6) whereas red solid symbols show early types (cr ≥ 2.6; see, e.g., Strateva et al. 2001; Blanton et al. 2003, for more discussion of cr as a morphological indicator). The red line shows a fit to the red sequence, and the blue line the adopted cut between red sequence and blue galaxies. U −V colors and M V values were synthesized using the observed ugr magnitudes for a 14 < r < 16.5 apparent magnitude limited sample, from which galaxies were randomly drawn weighted by 1/Vmax to approximate a volume limited sample of galaxies. Only galaxies with M V − 5 log 10 h < −18 were chosen to approximate the magnitude limit of the z = 0.7 sample of 1492 COMBO-17 galaxies. b) The morphologies of GEMS 0.65 ≤ z ≤ 0.75 galaxies, using the Sérsic n parameter as the morphological classifier. Filled red circles denote early-type galaxies with n ≥ 2.5, and open blue circles late-types with n < 2.5. Black crosses denote galaxies which were not successfully fit by either GALFIT or GIM2D. The solid lines denote fits to the red sequence (red) and the adopted separation between red and blue galaxies (blue), as in panel a). The inset panel shows the n distributions of the visually-classified E/S0 galaxies (red), Sb-Sdm galaxies (blue), and Sa galaxies (yellow). A cut at n = 2.5 clearly separates early-type and late-type galaxies with 80% reliability and less than 25% contamination. The inclusion of Sa galaxies in either of the late or early-type galaxy bins does not significantly affect this conclusion. c) The visual classifications of the GEMS z ∼ 0.7 galaxies. Red circles denote visually-classified E/S0 galaxies, green ellipses are Sa-Sm galaxies, blue stars are Peculiar/Strong Interaction galaxies, purple circles are Irregular/Weak Interaction and compact galaxies. We show also color postage stamps of red sequence galaxies: the top three lines are visually classified as E or S0 (where we show an unrepresentatively large fraction of E/S0s with substructure), the next two lines are classified as Sa-Sm, and the final line of galaxies are classified as Peculiar/Strong Interaction. Postage stamps are 6 ′′ square, corresponding to 35 kpc in the adopted cosmology.
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We have used the 30' x 30' Hubble Space Telescope image mosaic from the Galaxy Evolution from Morphology and Spectral energy distributions ( GEMS) project in conjunction with the COMBO-17 deep photometric redshift survey to define a sample of nearly 1500 galaxies with 0.65 less than or equal to z less than or equal to 0.75. With this sample, we can...
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Citations
... There is an observational agreement, up to a redshift of z ∼ 1, where early types as compared to spirals and irregulars, are massive, luminous, red, and old (Bell et al. 2003b ;Bolzonella et al. 2010 ;Pozzetti et al. 2010 ). Early-type galaxies which are supported by their rotation are approximately 60 per cent with no significant change from a redshift of approximately z ∼ 0 to ∼ 1 according to Van Der Wel & Van Der Marel ( 2008 ). ...
Evolution of galaxies is known to be influenced by a number of factors such as the environment that hosts the galaxy as well as the galaxies intrinsic properties. The environmental effects on galaxy properties have not been fully quantified. In our study, we analysed a sample of isolated galaxies within 0.005 < z < 0.080 from Sloan Digital Sky Survey data release 16, as part of a Digital Survey Isolated Galaxies catalogue. The aim was to investigate intrinsic physical properties of singly isolated galaxies in low density environment. We investigated the galaxies morphology, colour, luminosity, stellar masses and star-formation rates. A Concentration Index, Cr, of 2.65 separates our isolated sample into early- and late-type, with the late-types (spiral galaxies) dominating the isolated sample at 68% as confirmed from the visually classified sample obtained from galaxy zoo. Our isolated ellipticals are redder, massive and more luminous, while the isolated spirals are blue, less massive and less luminous. Both the isolated spirals and ellipticals have steeper colour relations indicating a fast transition to the red sequence. In the colour-colour analysis, most ellipticals were quiescent with the majority of spirals being star forming. 5% of the isolated ellipticals have recently quenched their star formation and are transiting to the red sequence. The isolated spirals experiences higher star forming activities, with a small fraction of passively evolving high mass isolated spirals. Similarly, isolated ellipticals exhibit low star formation rates (SFRs) indicating passive evolution, with a fraction being actively star forming.
... Subsequent research into colour bimodality has validated the findings of Strate v a et al. ( 2001 ) and Baldry et al. ( 2004b ) to at least z < 2 (e.g. Balogh et al. 2004 ;Bell et al. 2004 ;Williams et al. 2009 ;Taylor et al. 2015 ;Foltz et al. 2018 ). The colour bimodality is interesting to theorists as well because colour has a direct relation with star formation history. ...
... Taylor et al. 2015 ). Studies of this bimodality at different redshifts have revealed another interesting finding-although the populations are roughly equi v alent in total stellar mass at z ∼ 1, the red population has nearly doubled in stellar mass, stellar mass density, and number density o v er the past ∼7 Gyr (e.g Bell et al. 2004 ;Arnouts et al. 2007 ;Foltz et al. 2018 ). This suggests that galaxies mo v e between the two populations-these are two evolutionary stages. ...
Galaxy populations are known to exhibit a strong colour bimodality, corresponding to blue star-forming and red quiescent subpopulations. The relative abundance of the two populations has been found to vary with stellar mass and environment. In this paper, we explore the effect of environment considering different types of measurements. We choose a sample of 49 911 galaxies with 0.05 < z < 0.18 from the Galaxy And Mass Assembly survey. We study the dependence of the fraction of red galaxies on different measures of the local environment as well as the large-scale `geometric’ environment defined by density gradients in the surrounding cosmic web. We find that the red galaxy fraction varies with the environment at fixed stellar mass. The red fraction depends more strongly on local environmental measures than on large-scale geometric environment measures. By comparing the different environmental densities, we show that no density measurement fully explains the observed environmental red fraction variation, suggesting the different measures of environmental density contain different information. We test whether the local environmental measures, when combined together, can explain all the observed environmental red fraction variation. The geometric environment has a small residual effect, and this effect is larger for voids than any other type of geometric environment. This could provide a test of the physics applied to cosmological-scale galaxy evolution simulations as it combines large-scale effects with local environmental impact.
... From an observational perspective, large optical imaging and spectroscopic surveys have in the past two decades well established that the cessation of star formation is one of the driving processes of galaxy evolution over the past 810 Gyr (Bell et al. 2004;Bundy et al. 2006;Faber et al. 2007). However, despite a rich history of studies, a full understanding of the way in which star formation shuts down remains elusive. ...
We complement the MALATANG sample of dense gas in nearby galaxies with archival observations of ¹² CO and its isotopologues to determine scaling relations between Wide-field Infrared Survey Explorer (WISE) 12 μ m emission and molecular gas tracers at subkiloparsec scales. We find that 12 μ m luminosity is more tightly correlated with ¹² CO than it is with ¹³ CO or dense gas tracers. Residuals between predicted and observed ¹² CO are only weakly correlated with molecular gas mass surface density (Σ mol ) in regions where Σ mol is very low (∼10 M ⊙ pc ⁻² ). Above this limit, the ¹² CO residuals show no correlations with physical conditions of molecular gas, while ¹³ CO residuals depend on the gas optical depth and temperature. By analyzing differences from galaxy to galaxy, we confirm that the ¹² CO−12 μ m relation is strong and statistically robust with respect to star-forming galaxies and active galactic nucleus hosts. These results suggest that WISE 12 μ m emission can be used to trace total molecular gas instead of dense molecular gas, likely because polycyclic aromatic hydrocarbons (PAHs, a major contributor to WISE 12 μ m emission) may be well mixed with the gas that is traced by ¹² CO. We propose that WISE 12 μ m luminosity can be used to estimate molecular gas surface density for statistical analyses of the star formation process in galaxies.
... Galaxies have long been known to exhibit a bimodality in their star formation rates (SFRs) such that the population of bluer galaxies with higher SFRs make up the 'star-forming main sequence' and the redder galaxies with lower SFRs forming the quiescent 'red sequence' (e.g. Bell et al. 2004;Brinchmann et al. 2004;Brammer et al. 2011;Muzzin et al. 2012). The quiescent fraction increases strongly with increasing galaxy stellar mass, likely due to some internal ('mass') quenching process, as well as increasing with the density of its surrounding environment (e.g. ...
We forward-model mass-weighted ages (MWAs) and quiescent fractions in projected phase space (PPS), using data from the Sloan Digital Sky Survey, to jointly constrain an infall quenching model for galaxies in $\log(M_{\mathrm{vir}}/\mathrm{M}_{\odot})>14$ galaxy clusters at $z\sim 0$. We find the average deviation in MWA from the MWA-$M_\star$ relation depends on position in PPS, with a maximum difference between the inner cluster and infalling interloper galaxies of $\sim 1$ Gyr. Our model employs infall information from N-body simulations and stochastic star-formation histories from the UniverseMachine model. We find total quenching times of $t_\mathrm{Q}=3.7\pm 0.4$ Gyr and $t_\mathrm{Q}=4.0\pm 0.2$ Gyr after first pericentre, for $9<\log(M_{\star}/\mathrm{M}_{\odot})<10$ and $10<\log(M_{\star}/\mathrm{M}_{\odot})<10.5$ galaxies, respectively. By using MWAs, we break the degeneracy in time of quenching onset and timescale of star formation rate (SFR) decline. We find that time of quenching onset relative to pericentre is $t_{\mathrm{delay}}=3.5^{+0.6}_{-0.9}$ Gyr and $t_{\mathrm{delay}}=-0.3^{+0.8}_{-1.0}$ Gyr for our lower and higher stellar mass bins, respectively, and exponential SFR suppression timescales are $\tau_{\mathrm{env}}\leq 1.0$ Gyr and $\tau_{\mathrm{env}}\sim 2.3$ Gyr for our lower and higher stellar mass bins, respectively. Stochastic star formation histories remove the need for rapid infall quenching to maintain the bimodality in the SFR of cluster galaxies; the depth of the green valley prefers quenching onsets close to first pericentre and a longer quenching envelope, in slight tension with the MWA-driven results. Taken together these results suggest that quenching begins close to, or just after pericentre, but the timescale for quenching to be fully complete is much longer and therefore ram-pressure stripping is not complete on first pericentric passage.
... Previous large-scale surv e ys of galaxies have revealed a bimodality in the colour-magnitude diagram of galaxies with two distinct populations: one with blue optical colours and another with red optical colours (Strate v a et al. 2001 ;Baldry et al. 2004Baldry et al. , 2006Bell et al. 2004 ;Willmer et al. 2006 ;Faber et al. 2007 ;Martin et al. 2007 ;E-mail: dominic.smith@louisville.edu (DS); lori.porter@louisville.edu ...
... Graham et al. 2017 ). Green-valley galaxies have therefore long been thought of as the 'crossroads' of galaxy evolution, a transitional population between the two main galactic stages of the star-forming blue cloud and the 'red and dead' sequence (Bell et al. 2004 ;Faber et al. 2007 ;Martin et al. 2007 ;Mendez et al. 2011 ;Schawinski et al. 2014 ;Pan et al. 2015 ;Graham 2019 ); ho we ver, it is possible that these are also redsequence galaxies that have been rejuvenated (Graham et al. 2015(Graham et al. , 2017. ...
Galaxies fall broadly into two categories: star-forming (blue) galaxies and quiescent (red) galaxies. In between, one finds the less populated ‘green valley’. Some of these galaxies are suspected to be in the process of ceasing their star formation through a gradual exhaustion of gas supply, or already dead and experiencing a rejuvenation of star formation through fuel injection. We use the Galaxy And Mass Assembly (GAMA) database and the Galaxy Zoo citizen science morphological estimates to compare the morphology of galaxies in the green valley with those in the red sequence and blue cloud. Our goal is to examine the structural differences within galaxies that fall in the green valley, and what brings them there. Previous results found that disc features such as rings and lenses are more prominently represented in the green-valley population. We revisit this with a similar sized data set of galaxies with morphology labels provided by the Galaxy Zoo for the GAMA fields based on new Kilo-Degree Survey (KiDS) images. Our aim is to compare the results from expert classification qualitatively with those of citizen science. We observe that ring structures are indeed found more commonly in green-valley galaxies compared with their red and blue counterparts. We suggest that ring structures are a consequence of disc galaxies in the green valley actively exhibiting the characteristics of fading discs and evolving disc morphology of galaxies. We note that the progression from blue to red correlates with loosening spiral-arm structure.
... Subsequent research into colour bimodality has validated the findings of Strateva et al. (2001) and Baldry et al. (2004b) to at least < 2 (e.g. Balogh et al. 2004;Bell et al. 2004;Williams et al. 2009;Taylor et al. 2015;Foltz et al. 2018). The colour bimodality is interesting to theorists as well because colour has a direct relation with star formation history. ...
... Taylor et al. 2015). Studies of this bimodality at different redshifts have revealed another interesting finding -although the populations are roughly equivalent in total stellar mass at ∼ 1, the red population has nearly doubled in stellar mass, stellar mass density, and number density over the past ∼ 7 Gyr (e.g Bell et al. 2004;Arnouts et al. 2007;Foltz et al. 2018). This suggests that galaxies move between the two populations -these are two evolutionary stages. ...
Galaxy populations are known to exhibit a strong colour bimodality, corresponding to blue star-forming and red quiescent subpopulations. The relative abundance of the two populations has been found to vary with stellar mass and environment. In this paper, we explore the effect of environment considering different types of measurements. We choose a sample of 49, 911 galaxie with $0.05 < z < 0.18$ from the Galaxy And Mass Assembly survey. We study the dependence of the fraction of red galaxies on different measures of the local environment as well as the large-scale "geometric" environment arXiv:1412.2141 [astro-ph.CO] defined by density gradients in the surrounding cosmic web. We find that the red galaxy fraction varies with the environment independently of stellar mass. The local environmental measures exhibit a larger variation in red fraction from lower to higher density, as compared to the geometric environment. By comparing the different environmental densities pairwise, we show that no density measurement fully explains the observed environmental red fraction variation, suggesting the different densities contain different information. We test whether the local environmental measures, when combined together, can explain all the observed environmental red fraction variation. The geometric environment has a small residual effect, and this effect is larger for voids than any other type of geometric environment. This could provide a test of the physics applied to cosmological-scale galaxy evolution simulations as it combines large-scale effects with local environmental impact.
... Bell et al. 2004b;Brinchmann et al. 2004;Brammer et al. 2011;Muzzin et al. 2012) and a corresponding bimodality in the distribution of restframe colours (e.g. Strateva et al. 2001;Baldry et al. 2004;Bell et al. 2004a;Williams et al. 2009;Foltz et al. 2018;Muzzin et al. 2013b;Taylor et al. 2015). Observations of these two populations at different redshifts show that the number density and shape of the stellar mass function (SMF) for quiescent (red) galaxies has evolved dramatically, while the SMF of star-forming (blue) galaxies has remained nearly unchanged since ∼ 3.5 (e.g. ...
We use photometric redshifts and statistical background subtraction to measure stellar mass functions in galaxy group-mass ($4.5-8\times10^{13}~\mathrm{M}_\odot$) haloes at $1<z<1.5$. Groups are selected from COSMOS and SXDF, based on X-ray imaging and sparse spectroscopy. Stellar mass ($M_{\mathrm{stellar}}$) functions are computed for quiescent and star-forming galaxies separately, based on their rest-frame $UVJ$ colours. From these we compute the quiescent fraction and quiescent fraction excess (QFE) relative to the field as a function of $M_{\mathrm{stellar}}$. QFE increases with $M_{\mathrm{stellar}}$, similar to more massive clusters at $1<z<1.5$. This contrasts with the apparent separability of $M_{\mathrm{stellar}}$ and environmental factors on galaxy quiescent fractions at $z\sim 0$. We then compare our results with higher mass clusters at $1<z<1.5$ and lower redshifts. We find a strong QFE dependence on halo mass at fixed $M_{\mathrm{stellar}}$; well fit by a logarithmic slope of $\mathrm{d}(\mathrm{QFE})/\mathrm{d}\log (M_{\mathrm{halo}}) \sim 0.24 \pm 0.04$ for all $M_{\mathrm{stellar}}$ and redshift bins. This dependence is in remarkably good qualitative agreement with the hydrodynamic simulation BAHAMAS, but contradicts the observed dependence of QFE on $M_{\mathrm{stellar}}$. We interpret the results using two toy models: one where a time delay until rapid (instantaneous) quenching begins upon accretion to the main progenitor ("no pre-processing") and one where it starts upon first becoming a satellite ("pre-processing"). Delay times appear to be halo mass dependent, with a significantly stronger dependence required without pre-processing. We conclude that our results support models in which environmental quenching begins in low-mass ($<10^{14}M_\odot$) haloes at $z>1$.
... An additional piece of the puzzle is the correlation between galaxy color (and morphology) with both local environment and stellar mass [11,38,104]. The environmental dependence seems to indicate that not only internal, but also external, physical processes play a role in shaping the star formation of galaxies at all cosmic ages [18,22]. ...
With this paper we participate to the call for ideas issued by the European Space Agency to define the Science Program and plan for space missions from 2035 to 2050. In particular we present five science cases where major advancements can be achieved thanks to space-based spectroscopic observations at ultraviolet (UV) wavelengths. We discuss the possibility to (1) unveil the large-scale structures and cosmic web in emission at redshift $\lesssim 1.7$ ≲ 1.7 ; (2) study the exchange of baryons between galaxies and their surroundings to understand the contribution of the circumgalactic gas to the evolution and angular-momentum build-up of galaxies; (3) constrain the efficiency of ram-pressure stripping in removing gas from galaxies and its role in quenching star formation; (4) characterize the progenitor population of core-collapse supernovae to reveal the explosion mechanisms of stars; (5) target accreting white dwarfs in globular clusters to determine their evolution and fate. These science themes can be addressed thanks to UV (wavelength range $\lambda \sim 90 - 350$ λ ∼ 90 − 350 nm) observations carried out with a panoramic integral field spectrograph (field of view $\sim \!1 \times 1$ ∼ 1 × 1 arcmin ² ), and medium spectral (R = 4000) and spatial ( $\sim \!1^{\prime \prime } - 3^{\prime \prime }$ ∼ 1 ′ ′ − 3 ′ ′ ) resolution. Such a UV-optimized instrument will be unique in the coming years, when most of the new large facilities such as the Extremely Large Telescope and the James Webb Space Telescope are optimized for infrared wavelengths.
... Galaxies show bimodal distributions in fundamental properties, such as colours and structure, both locally (e.g., Strateva et al. 2001;Blanton et al. 2003;Baldry et al. 2004;Kauffmann et al. 2003) and out to at least z ∼ 2, (e.g., Bell et al. 2004;Willmer et al. 2006;Whitaker et al. 2011;Wuyts et al. 2011;Bell et al. 2012;Cheung et al. 2012;Muzzin et al. 2013). Moreover, there is strong evidence that there is continuous growth in the number density and stellar mass of the red and passively evolving early-type population from z∼ 1−2 to the present (e.g., Bell et al. 2004;Faber et al. 2007;Pozzetti et al. 2010;Ilbert et al. 2013). ...
... Galaxies show bimodal distributions in fundamental properties, such as colours and structure, both locally (e.g., Strateva et al. 2001;Blanton et al. 2003;Baldry et al. 2004;Kauffmann et al. 2003) and out to at least z ∼ 2, (e.g., Bell et al. 2004;Willmer et al. 2006;Whitaker et al. 2011;Wuyts et al. 2011;Bell et al. 2012;Cheung et al. 2012;Muzzin et al. 2013). Moreover, there is strong evidence that there is continuous growth in the number density and stellar mass of the red and passively evolving early-type population from z∼ 1−2 to the present (e.g., Bell et al. 2004;Faber et al. 2007;Pozzetti et al. 2010;Ilbert et al. 2013). This implies that a large fraction of late-type galaxies convert into early-types, due to the suppression of star formation (hereafter quenching) that accompanies their change in morphologies (e.g., Drory et al. 2004;Faber et al. 2007;Peng et al. 2010;Pozzetti et al. 2010;Tacchella et al. 2015;Woo et al. 2015). ...
Galaxy mergers are traditionally one of the favoured mechanisms for quenching star formation. To test this paradigm in the context of modern cosmological simulations, we use the IllustrisTNG simulation to investigate the impact of individual merger events on quenching (i.e. star formation rate at least 3sig below the star-forming main sequence) within 500Myr after the coalescence phase.The rate of quenching amongst recently merged galaxies is compared with a control sample that is matched in redshift, stellar mass, star formation rate (SFR), black hole mass and environment.We find quenching to be uncommon among the descendants of post-merger galaxies, with only 5% of galaxies quenching within 500 Myr after the merger.Despite this low absolute rate, we find that quenching occurs in post-mergers at twice the rate of the control galaxies.The fraction of quenched post-merger descendants 1.5 Gyr after the merger becomes statistically indistinguishable from that of non-post-mergers, suggesting that mergers could speed up the quenching process in those post-mergers whose progenitors had physical conditions able to sustain effective active galactic nuclei (AGN) kinetic feedback, thus capable of removing gas from galaxies.Our results indicate that although quenching does not commonly occur promptly after coalescence, mergers nonetheless do promote the cessation of star formation in some post-mergers. We find that, in IllustrisTNG, it is the implementation of the AGN kinetic feedback that is responsible for quenching post-mergers, as well as non-post-merger controls.As a result of the released kinetic energy, galaxies experience gas loss and eventually, they will quench.Galaxies with an initially low gas fraction show a preferable pre-disposition towards quenching.The primary distinguishing factor between quenched and star-forming galaxies is gas fraction, with a sharp boundary at fgas=0.1 in TNG.
... It has been established that the distribution of colours of galaxies is bimodal, with star-forming galaxies belonging to the 'blue cloud' and quiescent galaxies belonging to the 'red sequence' (Strateva et al. 2001;Bell et al. 2004). The redshift evolution of galaxy populations suggests that the quenching of star-formation is the likely process which moves a galaxy from the blue cloud to the red sequence (Baldry et al. 2004;Faber et al. 2007). ...
By combining Ha flux measurements from the Sloan Digital Sky Survey (SDSS) with UV flux observations from the Galaxy Evolution Explorer (GALEX), we examine the environmental dependence (through central/satellite distinction) of the rapid quenching and rejuvenation of galaxies. Ha emissions trace the most massive stars, thereby indicating star-formation on timescales of ~ 10 Myr, while UV emission traces star-formation on timescales of ~ 100 Myr. These varying timescales are exploited to probe the most recent star-formation histories of galaxies. In this work, we define a class of transient galaxies which have UV emission typical of star formation but negligible Ha emission. We find that the occurrence of these transients has a strong stellar mass dependence in both the satellite and central population. However, while at stellar masses greater than M* ~ 10^10 Msun they occur with equal frequency regardless of environmental class, at lower stellar masses they are more common in satellites only, with an excess of about 1 per cent across all low stellar mass galaxies. These satellite transients also have a strong halo mass and group-centric radial dependence suggesting they are driven by an environmental process. Finally, we show that `rejuvenating' galaxies, those with Ha emission but not UV emission, are few in number and do not have a strong difference in their occurrence rate in centrals or satellites. These unique probes point to an environmental quenching mechanism which occurs on short timescales after the satellite has been in the group environment for a significant time -- consistent with `delayed-then-rapid' quenching.
