arXiv subjects

Hans Bohringer

Publications and source records attributed to Hans Bohringer.

5 recordsLinked to original sources

arXiv2025

Galaxies at the edges: a complete census of MACS J0416.1-2403 cluster

Numerous studies have established that the environment influences the physical properties of a galaxy. While gas inflows supply the fuel for SF, high density and temperature conditions suppress SF activity through various quenching processes. Investigations into large scale structures, such as filaments and overdense regions in the cluster outskirts, have focused on the low z. To move to intermediate z and explore galaxy pathways combined with environmental effects, it is crucial to join wide field spectroscopy and deep photometry. Our primary objective is to spectroscopically analyze the photometric overdensities observed by Estrada et al.(2023) in the outskirts of massive cluster MACS J0416.1-2403 (z=0.397), interpreted as evidence of ongoing group infall, i.e. the pre processing scenario, and to investigate the behavior of galaxies in the outskirts about their g-r color, Mstar, and local density, emphasizing the influence of the environment on galaxy evolution. We conducted a spectroscopic analysis out to 5.5R200, using the AAOmega spectrograph. The large FoV and depth allowed us to explore galaxies up to the cluster periphery and across a wide Mstar range, reaching down to the limit of dwarf galaxies. Redshifts were obtained through independent but comparable methods: Redrock, EZ, and Redmost. We identified 148 new spectroscopic cluster members from a sample of 1236 objects. We found 81 galaxies located in filamentary and overdense regions, supporting the role of filamentary infall in the cluster mass assembly history. Our analysis revealed that galaxies in high density regions are more massive, redder, and more passive, compared to galaxies in low density regions that appear to be bluer, less massive, and more SF. These findings underscore the significance of environmental effects and the role of pre processing in shaping galaxy properties before cluster infall.

astro-ph.GA↗

arXiv2021

The HST See Change Program: I. Survey Design, Pipeline, and Supernova Discoveries

The See Change survey was designed to make $z>1$ cosmological measurements by efficiently discovering high-redshift Type Ia supernovae (SNe Ia) and improving cluster mass measurements through weak lensing. This survey observed twelve galaxy clusters with the Hubble Space Telescope spanning the redshift range $z=1.13$ to $1.75$, discovering 57 likely transients and 27 likely SNe Ia at $z\sim 0.8-2.3$. As in similar previous surveys (Dawson et al. 2009), this proved to be a highly efficient use of HST for SN observations; the See Change survey additionally tested the feasibility of maintaining, or further increasing, the efficiency at yet higher redshifts, where we have less detailed information on the expected cluster masses and star-formation rates. We find that the resulting number of SNe Ia per orbit is a factor of $\sim 8$ higher than for a field search, and 45% of our orbits contained an active SN Ia within 22 rest-frame days of peak, with one of the clusters by itself yielding 6 of the SNe Ia. We present the survey design, pipeline, and SN discoveries. Novel features include fully blinded SN searches, the first random forest candidate classifier for undersampled IR data (with a 50% detection threshold within 0.05 magnitudes of human searchers), real-time forward-modeling photometry of candidates, and semi-automated photometric classifications and follow-up forecasts. We also describe the spectroscopic follow-up, instrumental in measuring host-galaxy redshifts. The cosmology analysis of our sample will be presented in a companion paper.

astro-ph.CO↗

arXiv2018

High entropy and evidence for a merger in the low surface brightness cluster Abell 2399

We present results of the X-ray analyses of the nearby cluster of galaxies Abell 2399 ($z=0.058$) using the XMM-Newton and Suzaku satellites. This cluster is classified as a low surface brightness (LSB) cluster. It has a bimodal structure in X-rays, and the X-ray-emission peaks are significantly offset from the peaks in gas temperature. By de-projecting the annular spectra, the temperature and electron density in the central $r<0.1r_{200}$ region are measured to be 3.6~keV and $1.4\times10^{-3}~{\rm cm^{-3}}$, respectively. This yields a very high gas entropy, $\sim 300~{\rm keV\,cm^{2}}$, in the central region, comparable to the values observed in other LSB clusters. The scaled entropy of Abell 2399 is the highest among the REXCESS cluster sample. The spatial distribution of the member galaxies exhibits multiple substructures, the locations of which are significantly different from those in the X-ray image. We discovered a clear discontinuity in the X-ray brightness and temperature distributions in the western gas clump, which provides evidence of the presence of a cold front. Therefore, our results strongly suggest that A2399 has experienced a merger and that the high central entropy originates from the merger activity.

astro-ph.HE↗

arXiv2013

The X-ray Properties of Optically Selected Clusters of Galaxies

We present the results of Chandra and Suzaku X-ray observations of nine moderate-redshift (0.16 < z < 0.42) clusters discovered via the Red-sequence Cluster Survey (RCS). Surface brightness profiles are fitted to beta models, gas masses are determined, integrated spectra are extracted within R2500, and X-ray temperatures and luminosities are inferred. The Lx-Tx relationship expected from self-similar evolution is tested by comparing this sample to our previous X-ray investigation of nine high-redshift (0.6 < z < 1.0) optically selected clusters. We find that optically selected clusters are systematically less luminous than X-ray selected clusters of similar X-ray temperature at both moderate and high-z. We are unable to constrain evolution in the Lx-Tx relation with these data, but find it consistent with no evolution, within relatively large uncertainties. To investigate selection effects, we compare the X-ray properties of our sample to those of clusters in the representative X-ray selected REXCESS sample, also determined within R2500. We find that while RCS cluster X-ray properties span the entire range of those of massive clusters selected by other methods, their average X-ray properties are most similar to those of dynamically disturbed X-ray selected clusters. This similarity suggests that the true cluster distribution might contain a higher fraction of disturbed objects than are typically detected in X-ray selected surveys.

astro-ph.CO↗

arXiv2001

Weak Lensing Measurements of 42 SDSS/RASS Galaxy Clusters

We present a lensing study of 42 galaxy clusters imaged in Sloan Digital Sky Survey (SDSS) commissioning data. Cluster candidates are selected optically from SDSS imaging data and confirmed for this study by matching to X-ray sources found independently in the ROSAT all sky survey (RASS). Five color SDSS photometry is used to make accurate photometric redshift estimates that are used to rescale and combine the lensing measurements. The mean shear from these clusters is detected to 2 h-1 Mpc at the 7-sigma level, corresponding to a mass within that radius of 4.2 +/- 0.6 x 10^14 h-1 M_sun. The shear profile is well fit by a power law with index -0.9 +/- 0.3, consistent with that of an isothermal density profile. This paper demonstrates our ability to measure ensemble cluster masses from SDSS imaging data.

astro-ph↗