arXiv subjects

Cory R. Wagner

Publications and source records attributed to Cory R. Wagner.

3 recordsLinked to original sources

arXiv2018

Stripping of the Hot Gas Halos in Member Galaxies of Abell 1795

The nearby cluster Abell 1795 is used as a testbed to examine whether hot gas in cluster galaxies is stripped by the ram pressure of the intracluster medium (ICM). The expected X-ray emission in and around Abell 1795 galaxies is likely dominated by the ICM, low-mass X-ray binaries, active galactic nuclei, and hot gas halos. In order to constrain these components, we use archival Chandra X-ray Observatory and Sloan Digital Sky Survey (SDSS) observations of Abell 1795 and identify 58 massive (M_star>10^10 M_sun) spectroscopic cluster members within 5 arcmin of the Chandra optical axis. X-ray images at 0.5-1.5 keV and 4-8 keV were created for each cluster member and then stacked into two clustercentric radius bins: inner (0.25<R/R_500<1) and outer (1<R/R_500<2.5). Surface brightness profiles of inner and outer cluster members are fit using Markov chain Monte Carlo sampling in order to generate model parameters and measure the 0.5-1.5 keV luminosities of each model component. Leveraging effective total Chandra exposure times of 3.4 and 1.7 Msec for inner and outer cluster members, respectively, we report the detection of hot gas halos, in a statistical sense, around outer cluster members. Outer members have 0.5-1.5 keV hot halo luminosities (L_X = 8.1(-3.5/+5)x10^39 erg/s) that are six times larger than the upper limit for inner cluster members (L_X < 1.3x10^39 erg/s). This result suggests that the ICM is removing hot gas from the halos of Abell 1795 members as they fall into the cluster.

astro-ph.GA↗

arXiv2016

The Evolution of Star Formation Activity in Cluster Galaxies Over $0.15<z<1.5$

We explore 7.5 billion years of evolution in the star formation activity of massive ($M_{\star}>10^{10.1}\,M_{\odot}$) cluster galaxies using a sample of 25 clusters over $0.15<z<1$ from the Cluster Lensing And Supernova survey with Hubble and 11 clusters over $1<z<1.5$ from the IRAC Shallow Cluster Survey. Galaxy morphologies are determined visually using high-resolution Hubble Space Telescope images. Using the spectral energy distribution fitting code CIGALE, we measure star formation rates, stellar masses, and 4000 Å break strengths. The latter are used to separate quiescent and star-forming galaxies (SFGs). From $z\sim1.3$ to $z\sim0.2$, the specific star formation rate (sSFR) of cluster SFGs and quiescent galaxies decreases by factors of three and four, respectively. Over the same redshift range, the sSFR of the entire cluster population declines by a factor of 11, from $0.48\pm0.06\;\mathrm{Gyr}^{-1}$ to $0.043\pm0.009\;\mathrm{Gyr}^{-1}$. This strong overall sSFR evolution is driven by the growth of the quiescent population over time; the fraction of quiescent cluster galaxies increases from $28^{+8}_{-19}\%$ to $88^{+5}_{-4}\%$ over $z\sim1.3\rightarrow0.2$. The majority of the growth occurs at $z\gtrsim0.9$, where the quiescent fraction increases by 0.41. While the sSFR of the majority of star-forming cluster galaxies is at the level of the field, a small subset of cluster SFGs have low field-relative star formation activity, suggestive of long-timescale quenching. The large increase in the fraction of quiescent galaxies above $z\sim0.9$, coupled with the field-level sSFRs of cluster SFGs, suggests that higher redshift cluster galaxies are likely being quenched quickly. Assessing those timescales will require more accurate stellar population ages and star formation histories.

astro-ph.GA↗

arXiv2014

Star Formation in High-Redshift Cluster Ellipticals

We measure the star formation rates (SFRs) of massive ($M_{\star}>10^{10.1}M_{\odot}$) early-type galaxies (ETGs) in a sample of 11 high-redshift ($1.0 < z < 1.5$) galaxy clusters drawn from the IRAC Shallow Cluster Survey (ISCS). We identify ETGs visually from Hubble Space Telescope imaging and select likely cluster members as having either an appropriate spectroscopic redshift or red sequence color. Mid-infrared SFRs are measured using Spitzer 24 $μ$m data for isolated cluster galaxies for which contamination by neighbors, and active galactic nuclei, can be ruled out. Cluster ETGs show enhanced specific star formation rates (sSFRs) compared to cluster galaxies in the local Universe, but have sSFRs more than four times lower than that of field ETGs at $1 < z < 1.5$. Relative to the late-type cluster population, isolated ETGs show substantially quenched mean SFRs, yet still contribute 12% of the overall star formation activity measured in $1 < z < 1.5$ clusters. We find that new ETGs are likely being formed in ISCS clusters; the fraction of cluster galaxies identified as ETGs increases from 34% to 56% from $z \sim 1.5 \rightarrow 1.25$. While the fraction of cluster ETGs that are highly star-forming ($\textrm{SFR}\geq26\ M_{\odot}$ yr$^{-1}$) drops from 27% to 10% over the same period, their sSFRs are roughly constant. All these factors taken together suggest that, particularly at $z\gtrsim1.25$, the events that created these distant cluster ETGs$-$likely mergers, at least among the most massive$-$were both recent and gas-rich.

astro-ph.GA↗