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![Stacked spectra, including both passive and star-forming galaxies, for the density and stellar-mass groupings of J0152.7 (left) and J1252.9 (right). Spectra of similar density and stellar mass in the two clusters show similar features in general, though with stronger [OII] and weaker 4000 Å breaks visible in J1252.9. All wavelengths shown are in the rest frame.](profile/Alessandro-Rettura/publication/237843132/figure/fig10/AS:383635480956934@1468477234632/Stacked-spectra-including-both-passive-and-star-forming-galaxies-for-the-density-and.png)
Stacked spectra, including both passive and star-forming galaxies, for the density and stellar-mass groupings of J0152.7 (left) and J1252.9 (right). Spectra of similar density and stellar mass in the two clusters show similar features in general, though with stronger [OII] and weaker 4000 Å breaks visible in J1252.9. All wavelengths shown are in the rest frame.
Source publication
We have compared stacked spectra of galaxies, grouped by environment and
stellar mass, among 58 members of the redshift z = 1.24 galaxy cluster RDCS
J1252.9-2927 (J1252.9) and 134 galaxies in the z = 0.84 cluster RX J0152.7-1357
(J0152.7). These two clusters are excellent laboratories to study how galaxies
evolve from star-forming to passive at z ~...
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Citations
... The H9 line index flattens to a moderately large value (∼4Å) at ages beyond ∼1 Gyr, whereas the H8 line index continues to decrease much more steeply with increasing age. This flattening of the H9 line index is caused by metal absorption, primarily Mg I (e.g., Bica & Alloin 1986;Serote Roos & Gonçalves 2004), at wavelengths very close to H9. Absorption by Mg I can be clearly seen in the spectra of late F-type stars, as showcased by Kauffmann et al. (2003); van Dokkum & Stanford (2003); Wild et al. (2007); Demarco et al. (2010); Nantais et al. (2013) for both stellar and galaxy spectra around these features. Contamination by metal absorption lines makes H9 less accurate, when compared with H8, as an indicator of stellar age, particularly at the middle central spiral and on the outer arm where contamination by metal absorption (from the old stellar population comprising the main body of NGC 1275) is expected to be more severe according to the two-SSP composite model (Section 4.2). ...
We address the nature and origin of a spiral disk at the center of NGC 1275, the giant elliptical galaxy at the center of the Perseus cluster, that spans a radius of $\sim$$5\,\rm kpc$. By comparing stellar absorption lines measured in long-slit optical spectra with synthetic spectra for single stellar populations, we find that fitting of these lines requires two stellar populations: (i) a very young population that peaks in radial velocity at $\pm 250 {\rm \, km \, s^{-1}}$ of the systemic velocity within a radius of $\sim$$720\,\rm pc$ of the nucleus, a $1\,\sigma$ velocity dispersion significantly lower than $140 {\rm \, km \, s^{-1}}$, and an age of $0.15 \pm 0.05 \rm\,Gyr$; and (ii) a very old population having a constant radial velocity with a radius corresponding to the systemic velocity, a much broader velocity dispersion of $\sim$$250 {\rm \, km \, s^{-1}}$, and an age of around $10\,\rm Gyr$. We attribute the former to a post-starburst population associated with the spiral disk, and the latter to the main stellar body of NGC 1275 along the same sight line. If the spiral disk is the remnant of a cannibalized galaxy, then its progenitor would have had to retain an enormous amount of gas in the face of intensive ram-pressure stripping so as to form a total initial mass in stars of $\sim 3 \times 10^9 \,M_\odot$. More likely, the central spiral originally comprised a gaseous body accreted over the distant past from a residual cooling flow, before experiencing a starburst $\sim$$0.15\,\rm Gyr$ ago to form its stellar body.
... The H9 line index flattens to a moderately large value (∼4 Å) at ages beyond ∼1 Gyr, whereas the H8 line index continues to decrease much more steeply with increasing age. This flattening of the H9 line index is caused by metal absorption, primarily Mg I (e.g., Bica & Alloin 1986;Serote Roos & Gonçalves 2004), at wavelengths very close to H9. Absorption by Mg I can be clearly seen in the spectra of late F-type stars, as showcased by Kauffmann et al. (2003), van Dokkum & Stanford (2003), Wild et al. (2007), Demarco et al. (2010), and Nantais et al. (2013) for both stellar and galaxy spectra around these features. Contamination by metal absorption lines makes H9 less accurate, when compared with H8, as an indicator of stellar age, particularly at the middle central spiral and on the outer arm where contamination by metal absorption (from the old stellar population comprising the main body of NGC 1275) is expected to be more severe according to the two-SSP composite model (Section 4.2). ...
We address the nature and origin of a spiral disk at the center of NGC 1275, the giant elliptical galaxy at the center of the Perseus cluster, that spans a radius of ∼5 kpc. By comparing stellar absorption lines measured in long-slit optical spectra with synthetic spectra for single stellar populations, we find that fitting of these lines requires two stellar populations: (i) a very young population that peaks in radial velocity at ±250 km s ⁻¹ of the systemic velocity within a radius of ∼720 pc of the nucleus, a 1 σ velocity dispersion significantly lower than 140 km s ⁻¹ , and an age of 0.15 ± 0.05 Gyr; and (ii) a very old population having a constant radial velocity with a radius corresponding to the systemic velocity, a much broader velocity dispersion of ∼250 km s ⁻¹ , and an age of around 10 Gyr. We attribute the former to a post-starburst population associated with the spiral disk, and the latter to the main stellar body of NGC 1275 along the same sight line. If the spiral disk is the remnant of a cannibalized galaxy, then its progenitor would have had to retain an enormous amount of gas in the face of intensive ram-pressure stripping so as to form a total initial mass in stars of ∼3 × 10 ⁹ M ⊙ . More likely, the central spiral originally comprised a gaseous body accreted over the distant past from a residual cooling flow, before experiencing a starburst ∼0.15 Gyr ago to form its stellar body.
... While there are pioneering studies of galaxy clusters at higher redshifts (e.g. z> 1; Strazzullo et al. 2006;Gobat et al. 2008;Snyder et al. 2012;Lotz et al. 2013;Martini et al. 2013;Nantais et al. 2013;Zeimann et al. 2013;Newman et al. 2014;Stanford et al. 2014;Nanayakkara et al. 2016;Nantais et al. 2017;Strazzullo et al. 2019), deep spectroscopic cluster studies of galaxies of all types for a range of halo masses do not currently exist, and the typical properties of cluster galaxies at this epoch are still unknown. ...
We present results on the environmental dependence of the star-forming galaxy main sequence in 11 galaxy cluster fields at 1.0 < z < 1.5 from the Gemini Observations of Galaxies in Rich Early Environments Survey (GOGREEN) survey. We use a homogeneously selected sample of field and cluster galaxies whose membership is derived from dynamical analysis. Using [$\rm{O{\small II}}$]-derived star formation rates (SFRs), we find that cluster galaxies have suppressed SFRs at fixed stellar mass in comparison to their field counterparts by a factor of 1.4 ± 0.1 (∼3.3σ) across the stellar mass range: 9.0 < log (M*/M⊙) < 11.2. We also find that this modest suppression in the cluster galaxy star-forming main sequence is mass and redshift dependent: the difference between cluster and field increases towards lower stellar masses and lower redshift. When comparing the distribution of cluster and field galaxy SFRs to the star-forming main sequence, we find an overall shift towards lower SFRs in the cluster population, and note the absence of a tail of high SFR galaxies as seen in the field. Given this observed suppression in the cluster galaxy star-forming main sequence, we explore the implications for several scenarios such as formation time differences between cluster and field galaxies, and environmentally induced star formation quenching and associated time-scales.
... While there are pioneering studies of galaxy clusters at higher redshifts, (e.g. z > 1; Strazzullo et al. 2006;Gobat et al. 2008;Snyder et al. 2012;Lotz et al. 2013;Zeimann et al. 2013;Martini et al. 2013;Nantais et al. 2013;Newman et al. 2014;Stanford et al. 2014;Nanayakkara et al. 2016;Nantais et al. 2017;Strazzullo et al. 2019), deep spectroscopic cluster studies of galaxies of all types for a range of halo masses do not currently exist, and the typical properties of cluster galaxies at this epoch are still unknown. ...
We present results on the environmental dependence of the star-forming galaxy main sequence in 11 galaxy cluster fields at $1.0 < z < 1.5$ from the Gemini Observations of Galaxies in Rich Early Environments Survey (GOGREEN) survey. We use a homogeneously selected sample of field and cluster galaxies whose membership is derived from dynamical analysis. Using [OII]-derived star formation rates (SFRs), we find that cluster galaxies have suppressed SFRs at fixed stellar mass in comparison to their field counterparts by a factor of 1.4 $\pm$ 0.1 ($\sim3.3\sigma$) across the stellar mass range: $9.0 < \log(M_{*} /M_{\odot}) < 11.2$. We also find that this modest suppression in the cluster galaxy star-forming main sequence is mass and redshift dependent: the difference between cluster and field increases towards lower stellar masses and lower redshift. When comparing the distribution of cluster and field galaxy SFRs to the star-forming main sequence, we find an overall shift towards lower SFRs in the cluster population, and note the absence of a tail of high SFR galaxies as seen in the field. Given this observed suppression in the cluster galaxy star-forming main sequence, we explore the implications for several scenarios such as formation time differences between cluster and field galaxies, and environmentally-induced star formation quenching and associated timescales.
... we wish to observe when the environment-dependent evolution of galaxies unfolds. At higher redshifts, the number fraction of low-SFR and quenched galaxies in denser environments decreases (Nantais et al. 2013;Lee et al. 2015;Kawinwanichakij et al. 2017;Pintos-Castro et al. 2019), until the SFR density of the universe reaches its peak at z∼2 (Hopkins & Beacom 2006;Madau & Dickinson 2014). ...
The ZFIRE survey has spectroscopically confirmed two proto-clusters using the MOSFIRE instrument on Keck I: one at z = 2.095 in COSMOS and another at z = 1.62 in UKIRT Infrared Deep Sky Survey (UDS). Here, we use an updated ZFIRE data set to derive the properties of ionized gas regions of proto-cluster galaxies by extracting fluxes from emission lines H β 4861 Å, [O iii ] 5007 Å, H α 6563 Å, [N ii ] 6585 Å, and [S ii ] 6716,6731 Å. We measure gas-phase metallicity of members in both proto-clusters using two indicators, including a strong-line indicator relatively independent of the ionization parameter and electron density. Proto-cluster and field galaxies in both UDS and COSMOS lie on the same Mass–Metallicity Relation with both metallicity indicators. We compare our results to recent IllustrisTNG results, which report no significant gas-phase metallicity offset between proto-cluster and field galaxies until z = 1.5. This is in agreement with our observed metallicities, where no offset is measured between proto-cluster and field populations. We measure tentative evidence from stacked spectra that indicate UDS high-mass proto-cluster and field galaxies have differing [O iii ]/H β ratios; however, these results are dependent on the sample size of the high-mass stacks.
... The cores of Lynx E and W are very different, Lynx E resembling the cores of very massive clusters at similar redshifts, e.g., RDCS J1252.9-2927 at z=1.24 (Nantais et al. 2013), and XMMU J2235.2-2557 at z=1.39 (Grützbauch et al. 2012), dominated by passive bulge-dominated galaxies, while Lynx W lacks a well-defined core of such galaxies. However, the passive bulge-dominated galaxies within R 500 of the Lynx W center appear similar to those in the Lynx E core. ...
... The indices CN3883 and CaHK are defined in Davidge & Clark (1994). For the high-order Balmer line index z H A we adopt the definition from Nantais et al. (2013). For D4000 we use a shorter red passband than that used in the standard definition. ...
Few detailed investigations of stellar populations in passive galaxies beyond z ≈ 1 are based on deep spectroscopic observations, due to the difficulty in obtaining such data. We present a study of stellar populations, structure, and mass-to-light ratios ( M/L ) of a large sample of bulge-dominated galaxies in the two z = 1.27 clusters Lynx E and Lynx W, based on deep ground-based optical spectroscopy combined with imaging from the Hubble Space Telescope . We find that Lynx E has a well-defined core of red passive galaxies, while Lynx W lacks such a core. If all the sample galaxies evolve similarly in size from z = 1.27 to the present, the data would allow only 0.1 dex size growth at a fixed dynamical mass. However, to link the Lynx central galaxies to brightest cluster galaxies similar to those of low-redshift clusters, the Lynx galaxies would have to grow by at least a factor 5, possibly through major merging. The M/L ratios and the Balmer absorption lines of the Lynx galaxies are consistent with passive evolution of the stellar populations from z = 1.27 to the present and support ages of 1–3 Gyr. The galaxies in the outskirts of the clusters contain younger stellar populations than found in the cluster cores. However, when evolved passively to z ≈ 0 both populations are consistent with the observed populations in the Coma cluster galaxies. The bulge-dominated emission line galaxies in the clusters are dominated by stellar populations with subsolar metallicities. Thus, additional enrichment of these is required to produce Coma-like stellar populations by z ≈ 0.
... Absorption-line indices were determined using the Lick/IDS passband definitions ). In addition, we derive the indices CN3883 and CaHK (Davidge & Clark 1994) and D4000 (Bruzual 1983), the higher-order Balmer line indices Hδ A and Hγ A (Worthey & Ottaviani 1997), the Hβ G index defined by Jørgensen (1997), and the higher-order Balmer line index Hζ A (Nantais et al. 2013). In all cases, we first convolve the spectra to the Lick/IDS resolution in the rest frame of the galaxies; cf. ...
In order to study stellar populations and galaxy structures at intermediate and high redshift (z = 0.2-2.0) and link these properties to those of low-redshift galaxies, there is a need for well-defined local reference samples. Especially for galaxies in massive clusters, such samples are often limited to the Coma cluster galaxies. We present consistently calibrated velocity dispersions and absorption-line indices for galaxies in the central 2 R 500 ×2 R 500 of four massive clusters at z < 0.1: Abell 426/Perseus, Abell 1656/Coma, Abell 2029, and Abell 2142. The measurements are based on data from the Gemini Observatory, McDonald Observatory, and Sloan Digital Sky Survey. For bulge-dominated galaxies, the samples are 95% complete in Perseus and Coma and 74% complete in A2029 and A2142, to a limit of M B,abs ≤ -18.5 mag. The data serve as the local reference for our studies of galaxy populations in the higher-redshift clusters that are part of the Gemini/HST Galaxy Cluster Project (GCP). We establish the scaling relations between line indices and velocity dispersions as a reference for the GCP. We derive stellar population parameters, ages, metallicities [M/H], and abundance ratios from line indices, both averaged in bins of velocity dispersion and from individual measurements for galaxies in Perseus and Coma. The zero points of relations between the stellar population parameters and the velocity dispersions limit the allowed cluster-to-cluster variation of the four clusters to ±0.08 dex in age, ±0.06 dex in [M/H], ±0.07 dex in [CN/Fe], and ±0.03 dex in [Mg/Fe]. © 2018. The American Astronomical Society. All rights reserved.
... How and when the most massive galaxies assemble their stellar mass, stop forming stars, and acquire their observed morphologies remain outstanding questions. The redshift range 1.4 < z < 2 is a key epoch in this respect: elliptical galaxies start to become the dominant population in cluster cores, and star formation in spiral galaxies is being quenched (e.g., Blakeslee et al. 2006;Rosati et al. 2009;Mei et al. 2009;Overzier et al. 2009;Rettura et al. 2010Rettura et al. , 2011Raichoor et al. 2011;Strazzullo et al. 2010;Stanford et al. 2012;Snyder et al. 2012;Zeimann et al. 2012;Mei et al. 2012;Nantais et al. 2013). Interestingly, some field galaxy studies find that the star formation rate (SFR)-density relation reverses at z = 1 relative to z = 0 (Cooper et al. 2007; Elbaz et al. 2007), such that star formation no longer decreases with increasing galaxy density at z = 1. ...
We present 279 galaxy cluster candidates at z > 1.3 selected from the 94 deg2 Spitzer South Pole Telescope Deep Field (SSDF) survey. We use a simple algorithm to select candidate high-redshift clusters of galaxies based on Spitzer/IRAC mid-infrared data combined with shallow all-sky optical data. We identify distant cluster candidates adopting an overdensity threshold that results in a high purity (80%) cluster sample based on tests in the Spitzer Deep, Wide-Field Survey of the Boötes field. Our simple algorithm detects all three 1.4 < z ≤ 1.75 X-ray detected clusters in the Boötes field. The uniqueness of the SSDF survey resides not just in its area, one of the largest contiguous extragalactic fields observed with Spitzer, but also in its deep, multi-wavelength coverage by the South Pole Telescope (SPT), Herschel/SPIRE, and XMM-Newton. This rich data set will allow direct or stacked measurements of Sunyaev-Zel'dovich effect decrements or X-ray masses for many of the SSDF clusters presented here, and enable a systematic study of the most distant clusters on an unprecedented scale. We measure the angular correlation function of our sample and find that these candidates show strong clustering. Employing the COSMOS/UltraVista photometric catalog in order to infer the redshift distribution of our cluster selection, we find that these clusters have a comoving number density and a spatial clustering correlation scale length r 0 = (32 ± 7) h –1 Mpc. Assuming our sample is comprised of dark matter halos above a characteristic minimum mass, M min, we derive that at z = 1.5 these clusters reside in halos larger than . We find that the mean mass of our cluster sample is equal to ; thus, our sample contains the progenitors of present-day massive galaxy clusters.
We calculate H α-based star formation rates and determine the star formation rate–stellar mass relation for members of three Spitzer Adaptation of the Red-Sequence Cluster Survey (SpARCS) clusters at z ∼ 1.6 and serendipitously identified field galaxies at similar redshifts to the clusters. We find similar star formation rates in cluster and field galaxies throughout our range of stellar masses. The results are comparable to those seen in other clusters at similar redshifts, and consistent with our previous photometric evidence for little quenching activity in clusters. One possible explanation for our results is that galaxies in our z ∼ 1.6 clusters have been accreted too recently to show signs of environmental quenching. It is also possible that the clusters are not yet dynamically mature enough to produce important environmental quenching effects shown to be important at low redshift, such as ram-pressure stripping or harassment.
We calculate H$\alpha$-based star formation rates and determine the star formation rate-stellar mass relation for members of three SpARCS clusters at $z \sim 1.6$ and serendipitously identified field galaxies at similar redshifts to the clusters. We find similar star formation rates in cluster and field galaxies throughout our range of stellar masses. The results are comparable to those seen in other clusters at similar redshifts, and consistent with our previous photometric evidence for little quenching activity in clusters. One possible explanation for our results is that galaxies in our $z \sim 1.6$ clusters have been accreted too recently to show signs of environmental quenching. It is also possible that the clusters are not yet dynamically mature enough to produce important environmental quenching effects shown to be important at low redshift, such as ram pressure stripping or harassment.
