The GOGREEN Survey: A deep stellar mass function of cluster galaxies at 1.0 < z < 1.4 and the complex nature of satellite quenching

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Cold gas in the cosmic web around galaxy clusters

Damien Louis Alexandre Spérone-Longin

Galaxies live in very different types of environment. Those different environments are relics from the evolution of the Universe since the Big Bang. This network of structures observed via large scale surveys is called Cosmic Web. Within this web, galaxies can be isolated, in a filament, in a group, or in a cluster. When part of a cluster of galaxies, their morphologies, gas content (cold and hot), and star formation activities is seen to be affected by other galaxies, or by the gas inside the cluster. However, the long-term effects of the local environment on galaxy evolution remain unclear. Also, it has been observed that a pre-processing is happening long before the galaxies enter the cluster cores, which could explain the build-up of the passive galaxy sequence, where galaxies have quenched star formation. The aim of this thesis is to see if and how the cold molecular gas reservoir of galaxies is modified when star formation activity is decreasing and if there is a link with the position of the galaxy in the CW around the cluster. We gathered unprecedented observations: the first and largest survey of the molecular gas content of galaxies in and around the same cluster environment at intermediate redshifts. These Atacama Large Millimeter Array observations are part of a larger survey called Spatially Extended ESO Distant Cluster Survey. We are focusing on two clusters at a redshift of 0.5, which benefit from previous deep photometric and spectroscopic observations. This will allow us to derive accurate stellar masses and star formation rates, in order to compare those galaxies to other surveys of the cold gas content of galaxies, either in the field or inside different clusters. We unveiled a new population of galaxies with normal star formation rates but less cold molecular gas than other galaxies at the same stellar mass. This could be an indication that the gas reservoir responsible for the star formation changes either in mass or properties, before the star formation is affected. We also noticed that galaxies with the lowest cold-molecular-gas-to-stellar-mass ratios are preferentially either in the cluster core or in overdensities away from the cluster, confirming the existence of a pre-processing in overdensities surrounding the cluster. But active galaxies inside or close to the cluster, do not always have depleted CO reservoir. This thesis opens up new prospects on the study of the cold gas content of galaxies at intermediate redshift. It showed the necessity to observe galaxies that are in a transition regime between star forming and passive, in order to understand how star formation is suppressed around clusters. Those results could be extended to much larger samples, with the help of the upcoming new generation of instruments such as the Square Kilometer Array.

EPFL2021

Cold gas in the inner regions of intermediate redshift clusters

Pascale Jablonka

Determining the nature and modes of star formation at galactic scales requires an understanding of the relationship between the gas content of a galaxy and its star formation rate. Remarkable progress has been made in understanding the conversion mechanisms in field galaxies, but the cold and dense gas fueling the star formation in galaxies inside clusters has been investigated much less often. We present the first CO observations of luminous infrared galaxies (LIRGs) inside the virial radii of two intermediate redshift clusters, CL1416+4446 (z = 0.397) and CL0926+1242 (z = 0.489). We detect three galaxies at high significance (5 to 10 sigma), and provide robust estimates of their CO luminosities L'(CO). To put our results into a general context, we revisit the relation between cold and hot gas and stellar mass in nearby field and cluster galaxies. We find evidence that at fixed L-IR (or fixed stellar mass), the frequency of high L'(CO) galaxies is lower in clusters than in the field, suggesting environmental depletion of the reservoir of cold gas. The level of star formation activity in a galaxy is primarily linked to the amount of cold gas, rather than to the galaxy mass or the lookback time. In clusters, just as in the field, the conversion between gas and stars seems universal. The relation between L-IR and L'(CO) for distant cluster galaxies extends the relation of nearby galaxies to higher IR luminosities. Nevertheless, the intermediate redshift galaxies fall well within the dispersion of the trend defined by local systems. Considering that L'(CO) is generally derived from the CO(1-0) line and sensitive to the vast majority of the molecular gas in the cold interstellar medium of galaxies, but less to the part which will actually be used to form stars, we suggest that molecular gas can be stripped before the star formation rate is affected. Combining our sample with others, we find evidence for a decrease in CO towards the cluster centers. This is the first hint of an environmental impact on cold gas at intermediate redshift.

Edp Sciences S A2013

The GOGREEN survey: the environmental dependence of the star-forming galaxy main sequence at 1.0 < z < 1.5

Hung-Hsu Chan, Pascale Jablonka

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 [O 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 (similar to 3.3 sigma) across the stellar mass range: 9.0 < log (M-*/M-circle dot) < 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.