scholarly journals Molecular gas in two companion cluster galaxies at z = 1.2

2018 ◽  
Vol 617 ◽  
pp. A103 ◽  
Author(s):  
G. Castignani ◽  
F. Combes ◽  
P. Salomé ◽  
S. Andreon ◽  
M. Pannella ◽  
...  

Context. Probing both star formation history and evolution of distant cluster galaxies is essential to evaluate the effect of dense environment on shaping the galaxy properties we observe today. Aims. We investigate the effect of cluster environment on the processing of the molecular gas in distant cluster galaxies. We study the molecular gas properties of two star-forming galaxies separated by 6 kpc in the projected space and belonging to a galaxy cluster selected from the Irac Shallow Cluster Survey, at a redshift z = 1.2, that is, ~ 2 Gyr after the cosmic star formation density peak. This work describes the first CO detection from 1 < z < 1.4 star-forming cluster galaxies with no clear reported evidence of active galactic nuclei. Methods. We exploit observations taken with the NOEMA interferometer at ~3 mm to detect CO(2−1) line emission from the two selected galaxies, unresolved by our observations. Results. Based on the CO(2−1) spectrum, we estimate a total molecular gas mass M(H2) = (2.2+0.50.4) × 1010 M⊙, where fully excited gas is assumed, and a dust mass Mdust < 4.2 × 108 M⊙ for the two blended sources. The two galaxies have similar stellar masses and Hα-based star formation rates (SFRs) found in previous work, as well as a large relative velocity of ~400 km s−1 estimated from the CO(2−1) line width. These findings tend to privilege a scenario where both sources contribute to the observed CO(2−1). Using the archival Spitzer MIPS flux at 24 μm we estimate an SFR (24μm) = (28+12−8) M⊙/yr for each of the two galaxies. Assuming that the two sources contribute equally to the observed CO(2−1), our analysis yields a depletion timescale of τdep = (3.9+1.4−1.8) × 108 yr, and a molecular gas to stellar mass ratio of 0.17 ± 0.13 for each of two sources, separately. We also provide a new, more precise measurement of an unknown weighted mean of the redshifts of the two galaxies, z = 1.163 ± 0.001. Conclusions. Our results are in overall agreement with those of other distant cluster galaxies and with model predictions for main sequence (MS) field galaxies at similar redshifts. The two target galaxies have molecular gas mass and depletion times that are marginally compatible with, but smaller than those of MS field galaxies, suggesting that the molecular gas has not been sufficiently refueled. We speculate that the cluster environment might have played a role in preventing the refueling via environmental mechanisms such as galaxy harassment, strangulation, ram-pressure, or tidal stripping. Higher-resolution and higher-frequency observations will enable us to spatially resolve the two sources and possibly distinguish between different gas processing mechanisms.

2020 ◽  
Vol 635 ◽  
pp. A32 ◽  
Author(s):  
G. Castignani ◽  
F. Combes ◽  
P. Salomé ◽  
J. Freundlich

The mechanisms governing the stellar mass assembly and star formation history of brightest cluster galaxies (BCGs) are still being debated. By means of new and archival molecular gas observations we investigate the role of dense megaparsec-scale environments in regulating the fueling of star formation in distant BCGs, through cosmic time. We observed in CO with the IRAM 30 m telescope two star-forming BCGs belonging to SpARCS clusters, namely, 3C 244.1 (z = 0.4) and SDSS J161112.65+550823.5 (z = 0.9), and compared their molecular gas and star formation properties with those of a compilation of ∼100 distant cluster galaxies from the literature, including nine additional distant BCGs at z  ∼  0.4 − 3.5. We set robust upper limits of MH2 <  1.0 × 1010 M⊙ and < 2.8 × 1010 M⊙ to their molecular gas content, respectively, and to the ratio of molecular gas to stellar mass M(H2)/M⋆ ≲ 0.2 and depletion time τdep ≲ 40 Myr of the two targeted BCGs. They are thus among the distant cluster galaxies with the lowest gas fractions and shortest depletion times. The majority (64%±15% and 73%±18%) of the 11 BCGs with observations in CO have lower M(H2)/M⋆ values and τdep, respectively, than those estimated for main sequence galaxies. Statistical analysis also tentatively suggests that the values of M(H2)/M⋆ and τdep for the 11 BCGs deviates, with a significance of ∼2σ, from those of the comparison sample of cluster galaxies. A morphological analysis for a subsample of seven BCGs with archival HST observations reveals that 71%±17% of the BCGs are compact or show star-forming components or substructures. Our results suggest a scenario where distant star-forming BCGs assemble a significant fraction ∼16% of their stellar mass on the relatively short timescale ∼τdep, while environmental mechanisms might prevent the replenishment of gas feeding the star formation. We speculate that compact components also favor the rapid exhaustion of molecular gas and ultimately help to quench the BCGs. Distant star-forming BCGs are excellent targets for ALMA and for next-generation telescopes such as the James Webb Space Telescope.


2019 ◽  
Vol 624 ◽  
pp. A81 ◽  
Author(s):  
Allison W. S. Man ◽  
Matthew D. Lehnert ◽  
Joël D. R. Vernet ◽  
Carlos De Breuck ◽  
Theresa Falkendal

The objective of this work is to study how active galactic nuclei (AGN) influence star formation in host galaxies. We present a detailed investigation of the star-formation history and conditions of a z = 2.57 massive radio galaxy based on VLT/X-shooter and ALMA observations. The deep rest-frame ultraviolet spectrum contains photospheric absorption lines and wind features indicating the presence of OB-type stars. The most significantly detected photospheric features are used to characterize the recent star formation: neither instantaneous nor continuous star-formation history is consistent with the relative strength of the Si IIλ1485 and S Vλ1502 absorption. Rather, at least two bursts of star formation took place in the recent past, at 6+1-2 Myr and ≳20 Myr ago, respectively. We deduce a molecular H2 gas mass of (3.9 ± 1.0) × 1010 M⊙ based on ALMA observations of the [C I] 3P2−3P1 emission. The molecular gas mass is only 13% of its stellar mass. Combined with its high star-formation rate of (1020-170+190 M⊙ yr-1, this implies a high star-formation efficiency of (26 ± 8) Gyr−1 and a short depletion time of (38 ± 12) Myr. We attribute the efficient star formation to compressive gas motions in order to explain the modest velocity dispersions (⩽55 km s−1) of the photospheric lines and of the star-forming gas traced by [C I]. Because of the likely very young age of the radio source, our findings suggest that vigorous star formation consumes much of the gas and works in concert with the AGN to remove any residual molecular gas, and eventually quenching star formation in massive galaxies.


2020 ◽  
Vol 496 (1) ◽  
pp. 442-455 ◽  
Author(s):  
Kshitija Kelkar ◽  
K S Dwarakanath ◽  
Bianca M Poggianti ◽  
Alessia Moretti ◽  
Rogério Monteiro-Oliveira ◽  
...  

ABSTRACT We present a detailed analysis of star formation properties of galaxies in a nearby (z ∼ 0.046) young (∼0.6 Gyr) post-merger cluster system A3376, with a moderate merger shock front (vs ∼1630 km s−1; $\mathcal {M}$ ∼ 2) observed as symmetric radio relics. Exploiting the spectroscopic data from the wide-field OmegaWINGS survey and the associated photometric information, our investigations reveal the plausible effects of the dynamic post-merger environment differing from the high-density cluster environment experienced prior to the merging activity. The remnants of the pre-merger relaxed cluster environment are realized through the existence of passive spiral galaxies located in the central regions of the cluster between the two brightest cluster galaxies. We discover A3376 to contain a population of massive (log (M*/M⊙) &gt; 10) blue regular star-forming spirals in regions of maximum merger shock influence but exhibiting star formation rates similar to those in relaxed clusters at similar epoch. We further discover low-mass (log (M*/M⊙) ≤ 10) late-type blue post-starburst galaxies which could either be formed as a result of rapid quenching of low-mass spirals following the shock-induced star formation or due to the intense surge in the intracluster medium pressures at the beginning of the merger. With the possibility of the merger shock affecting high- and low-mass spirals differently, our results bridge the seemingly contradictory results observed in known merging cluster systems so far and establish that different environmental effects are at play right from pre- to post-merger stages.


2018 ◽  
Vol 615 ◽  
pp. A77 ◽  
Author(s):  
B. C. Lemaux ◽  
O. Le Fèvre ◽  
O. Cucciati ◽  
B. Ribeiro ◽  
L. A. M. Tasca ◽  
...  

Using spectroscopic observations taken for the Visible Multi-Object Spectrograph (VIMOS) Ultra-Deep Survey (VUDS) we report here on the discovery of PCl J1001+0220, a massive proto-cluster of galaxies located at zspec ~ 4.57 in the COSMOS field. With nine spectroscopic members, the proto-cluster was initially detected as a ~12σ spectroscopic overdensity of typical star-forming galaxies in the blind spectroscopic survey of the early universe (2 < z ≲ 6) performed by VUDS. It was further mapped using a new technique developed which statistically combines spectroscopic and photometric redshifts, the latter derived from a recent compilation of incredibly deep multi-band imaging performed on the COSMOS field. Through various methods, the descendant mass of PCl J1001+0220 is estimated to be log (Mh/M⊙)z=0 ~ 14.5–15 with a large amount of mass apparently already in place at z ~ 4.57. An exhaustive comparison was made between the properties of various spectroscopic and photometric member samples and matched samples of galaxies inhabiting less dense environments at the same redshifts. Tentative evidence is found for a fractional excess of older galaxies more massive in their stellar content amongst the member samples relative to the coeval field, an observation which suggests the pervasive early onset of vigorous star formation for proto-cluster galaxies. No evidence is found for the differences in the star formation rates (SFRs) of member and coeval field galaxies either through estimating by means of the rest-frame ultraviolet or through separately stacking extremely deep Very Large Array 3 GHz imaging for both samples. Additionally, no evidence for pervasive strong active galactic nuclei (AGN) activity is observed in either environment. Analysis of Hubble Space Telescope images of both sets of galaxies as well as their immediate surroundings provides weak evidence for an elevated incidence of galaxy–galaxy interaction within the bounds of the proto-cluster. The stacked and individual spectral properties of the two samples are compared, with a definite suppression of Lyα seen in the average member galaxy relative to the coeval field (fesc, Lyα = 1.8−1.7+0.3% and 4.0−0.8+1.0%, respectively). This observation along with other lines of evidence leads us to infer the possible presence of a large, cool, diffuse medium within the proto-cluster environment evocative of a nascent intracluster medium forming in the early universe.


2019 ◽  
Vol 15 (S359) ◽  
pp. 158-162
Author(s):  
Damien Spérone-Longin

AbstractDense environments have an impact on the star formation rate of galaxies. As stars form from molecular gas, looking at the cold molecular gas content of a galaxy gives useful insights on its efficiency in forming stars. However, most galaxies observed in CO (a proxy for the cold molecular gas content) at intermediate redshifts, are field galaxies. Only a handful of studies focused on cluster galaxies. I present new results on the environment of one medium mass cluster from the EDisCS survey at z ˜ 0.5. 27 star-forming galaxies were selected to evenly sample the range of densities encountered inside and around the cluster. We cover a region extending as far as 8 virial radii from the cluster center. Indeed there is ample evidence that star formation quenching starts already beyond 3 cluster virial radii. I discuss our CO(3-2) ALMA observations, which unveil a large fraction of galaxies with low gas-to-stellar mass ratios.


2021 ◽  
Vol 923 (2) ◽  
pp. L27
Author(s):  
N. Sulzenauer ◽  
H. Dannerbauer ◽  
A. Díaz-Sánchez ◽  
B. Ziegler ◽  
S. Iglesias-Groth ◽  
...  

Abstract Based on observations with the IRAM 30 m and Yebes 40 m telescopes, we report evidence of the detection of Milky Way–like, low-excitation molecular gas, up to the transition CO(J = 5–4), in a distant, dusty star-forming galaxy at z CO = 1.60454. WISE J122651.0+214958.8 (alias SDSS J1226, the Cosmic Seahorse), is strongly lensed by a foreground galaxy cluster at z = 0.44 with a source magnification of μ = 9.5 ± 0.7. This galaxy was selected by cross-correlating near-to-mid-infrared colors within the full-sky AllWISE survey, originally aiming to discover rare analogs of the archetypical strongly lensed submillimeter galaxy SMM J2135–0102, the Cosmic Eyelash. We derive an apparent (i.e., not corrected for lensing magnification) rest-frame 8–1000 μm infrared luminosity of μ L IR = 1.66 − 0.04 + 0.04 × 10 13 L ⊙ and apparent star formation rate μSFRIR = 2960 ± 70 M ⊙ yr−1. SDSS J1226 is ultrabright at S 350μm ≃ 170 mJy and shows similarly bright low-J CO line intensities as SMM J2135–0102, however, with exceptionally small CO(J = 5–4) intensity. We consider different scenarios to reconcile our observations with typical findings of high-z starbursts, and speculate about the presence of a previously unseen star formation mechanism in cosmic noon submillimeter galaxies. In conclusion, the remarkable low line luminosity ratio r 5,2 = 0.11 ± 0.02 is best explained by an extended, main-sequence star formation mode—representing a missing link between starbursts to low-luminosity systems during the epoch of peak star formation history.


2020 ◽  
Vol 493 (4) ◽  
pp. 5987-6000 ◽  
Author(s):  
Lyndsay J Old ◽  
Michael L Balogh ◽  
Remco F J van der Burg ◽  
Andrea Biviano ◽  
Howard K C Yee ◽  
...  

ABSTRACT We present results on the environmental dependence of the star-forming galaxy main sequence in 11 galaxy cluster fields at 1.0 &lt; z &lt; 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 &lt; log (M*/M⊙) &lt; 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.


2017 ◽  
Vol 602 ◽  
pp. A51 ◽  
Author(s):  
B. Vollmer ◽  
P. Gratier ◽  
J. Braine ◽  
C. Bot

High-z star-forming galaxies have significantly higher gas fractions and star-formation efficiencies per molecular gas mass than local star-forming galaxies. In this work, we take a closer look at the gas content or fraction and the associated star-formation rate in main sequence and starburst galaxies at z = 0 and z ~ 1–2 by applying an analytical model of galactic clumpy gas disks to samples of local spiral galaxies, ULIRGs, submillimeter (smm), and high-z star-forming galaxies. The model simultaneously calculates the total gas mass, Hi/H2 mass, the gas velocity dispersion, IR luminosity, IR spectral energy distribution, CO spectral line energy distribution (SLED), HCN(1–0) and HCO+(1–0) emission of a galaxy given its size, integrated star formation rate, stellar mass radial profile, rotation curve, and Toomre Q parameter. The model reproduces the observed CO luminosities and SLEDs of all sample galaxies within the model uncertainties (~0.3 dex). Whereas the CO emission is robust against the variation of model parameters, the HCN and HCO+ emissions are sensitive to the chemistry of the interstellar medium. The CO and HCN mass-to-light conversion factors, including CO-dark H2, are given and compared to the values found in the literature. All model conversion factors have uncertainties of a factor of two. Both the HCN and HCO+ emissions trace the dense molecular gas to a factor of approximately two for the local spiral galaxies, ULIRGs and smm-galaxies. Approximately 80% of the molecular line emission of compact starburst galaxies originates in non-self-gravitating gas clouds. The effect of HCN infrared pumping is small but measurable (10–20%). The gas velocity dispersion varies significantly with the Toomre Q parameter. The Q = 1.5 model yields high-velocity dispersions (vdisp ≫ 10 km s-1) consistent with available observations of high-z star-forming galaxies and ULIRGs. However, we note that these high-velocity dispersions are not mandatory for starburst galaxies. The integrated Kennicutt-Schmidt law has a slope of approximately 1 for the local spirals, ULIRGs, and smm-galaxies, whereas the slope is 1.7 for high-z star-forming galaxies. The model shows Kennicutt-Schmidt laws with respect to the molecular gas surface density with slopes of approximately 1.5 for local spiral galaxies, high-z star-forming galaxies. The relation steepens for compact starburst galaxies. The model star-formation rate per unit area is, as observed, proportional to the molecular gas surface density divided by the dynamical timescale. Our relatively simple analytic model together with the recipes for the molecular line emission appears to capture the essential physics of galactic clumpy gas disks.


2012 ◽  
Vol 8 (S295) ◽  
pp. 64-73 ◽  
Author(s):  
E. Daddi ◽  
M. T. Sargent ◽  
M. Béthermin ◽  
G. Magdis

AbstractRecent observations have revealed the existence of a ‘main sequence’ of star-forming galaxies out to high redshift. While the majority of star-forming galaxies are observed to be close to this relation between star formation rate (SFR) and stellar mass, a smaller subset of the population – so-called ‘starbursts’ – displays specific star-formation rates and star-formation efficiencies that exceed those of normal (main-sequence) galaxies by up to an order of magnitude. A large degree of homogeneity and similarity has been observed for the properties of the population of normal galaxies across a broad redshift range, including a narrow correlation between their CO luminosity (hence gas content) and IR luminosity and an almost invariable IR SED getting warmer with redshift, while starburst galaxies display systematically different properties. This can be used to devise a simple description of the evolution of the star-forming galaxy population since z ~ 2 and, with a higher degree of uncertainty, even further back in time, in a scheme that we dub two star formation mode framework (2-SFM). We show how this can successfully reproduce the shape of the IR luminosity function of galaxies as a function of redshifts, and the IR number counts. Furthermore, we can link the cosmic evolution of the sSFR of main-sequence galaxies to the evolution of the molecular fuel reservoir and to derive estimates of the molecular gas mass functions of star-forming galaxies that are based on their empirically measured gas properties rather than simulations or semi-analytical modelling. We also infer the evolution of the cosmic abundance of molecular gas and briefly discuss its expected observational signature by molecular line emission, the CO luminosity function.


2020 ◽  
Vol 496 (3) ◽  
pp. 3841-3861
Author(s):  
Sam P Vaughan ◽  
Alfred L Tiley ◽  
Roger L Davies ◽  
Laura J Prichard ◽  
Scott M Croom ◽  
...  

ABSTRACT Galaxy clusters have long been theorized to quench the star formation of their members. This study uses integral-field unit observations from the K-band MultiObject Spectrograph (KMOS) – Cluster Lensing And Supernova survey with Hubble (CLASH) survey (K-CLASH) to search for evidence of quenching in massive galaxy clusters at redshifts 0.3 &lt; z &lt; 0.6. We first construct mass-matched samples of exclusively star-forming cluster and field galaxies, then investigate the spatial extent of their H α emission and study their interstellar medium conditions using emission line ratios. The average ratio of H α half-light radius to optical half-light radius ($r_{\mathrm{e}, {\rm {H}\,\alpha }}/r_{\mathrm{e}, R_{\mathrm{c} } }$) for all galaxies is 1.14 ± 0.06, showing that star formation is taking place throughout stellar discs at these redshifts. However, on average, cluster galaxies have a smaller $r_{\mathrm{e}, {\rm {H}\alpha }}/r_{\mathrm{e}, R_{\mathrm{c} } }$ ratio than field galaxies: 〈$r_{\mathrm{e}, {\rm {H}\alpha }}/r_{\mathrm{e}, R_{\mathrm{c} } }$〉 = 0.96 ± 0.09 compared to 1.22 ± 0.08 (smaller at a 98 per cent credibility level). These values are uncorrected for the wavelength difference between H α emission and Rc-band stellar light but implementing such a correction only reinforces our results. We also show that whilst the cluster and field samples follow indistinguishable mass–metallicity (MZ) relations, the residuals around the MZ relation of cluster members correlate with cluster-centric distance; galaxies residing closer to the cluster centre tend to have enhanced metallicities (significant at the 2.6σ level). Finally, in contrast to previous studies, we find no significant differences in electron number density between the cluster and field galaxies. We use simple chemical evolution models to conclude that the effects of disc strangulation and ram-pressure stripping can quantitatively explain our observations.


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