Deep Hα survey of the Coma cluster: The Catalog

TL;DR

This study presents a deep wide-field narrow-band survey of the Coma cluster using the Wide Field Camera on the Isaac Newton Telescope to measure $H\alpha$+[N II] fluxes and equivalent widths down to dwarf galaxies across a ~2.5 deg$^2$ region. By combining field-specific continuum subtraction with robust astrometric and photometric calibration, the authors assemble a catalog of 124 spectroscopically confirmed Coma members with $H\alpha$ emission, of which many are newly detected. The H$\alpha$ luminosity function is derived after correcting for [N II] contamination and internal extinction, yielding a faint-end slope of $\alpha = -0.75 \pm 0.13$ and $\log L^* = 41.49 \pm 0.24$, in agreement with prior work and illustrating suppressed star formation in dwarf galaxies within this dense cluster. The results establish a benchmark for environmental effects on star formation in rich clusters and set the stage for forthcoming multi-wavelength analyses. The work demonstrates the power of deep, wide-field narrow-band surveys to probe low-SFR galaxies in cluster environments and provide a robust basis for comparison with less dense clusters and the field.

Abstract

We present a deep wide-field narrow-band imaging survey of the local rich and dynamically relaxed Coma cluster of galaxies, carried out with the Wide Field Camera at the Isaac Newton Telescope. The survey covers a region of about 2.5 sq. deg. extending from the core of the cluster out to the infall region over the south-west quadrant of the Coma cluster. The $R$ (6380~Å) and $[$S$\scriptstyle\rm II$$]$ (6725~Å) filters of WFC/INT were used to derive the H$α$+[N{\sc ii}] fluxes and equivalent widths of cluster galaxies distributed over a wide range of environmental conditions. The depth of our imaging observations allows us to measure reliably those properties well down into the dwarf regime in the Coma cluster for the first time. We have detected 124 H$α$ emitting sources with spectroscopically-determined membership, 96 of which have not been detected previously. In this paper, we report on the data analysis process and the methodology we used to measure reliable H$α$ properties, and present the measurement catalogue.

Figures (13)

• Figure 2: The filter throughputs ($R$ and $[$S$\rm II$$]$) and the spectrum of the observed standard spectrophotometric star, Hz21.
• Figure 3: The distribution of the magnitude shift for the point sources in the Coma-core1 pointing (see Tables \ref{['lisint']} and \ref{['lispo']}). Delta $R$-magnitudes is the difference between the SDSS magnitudes and that from SExtractor on our $R$-band images. About 50 percent of the point sources, which were found with starfind, were not confirmed by SDSS as stars. The blue solid histogram represents all point sources and the red dashed line shows the same for objects confirmed by SDSS as stars. The median of the Delta $R$-magnitudes is calculated to find the magnitude zero point. The final zero point of our images in the $R$-band is 25.1$\pm$0.2 mag.
• Figure 4: Left: Comparison of the $R$ magnitudes from Adami et al. (2006) with those from this study. The measurements agree within the RMS scatter of 0.19 mag. Right: The SDSS derived $R$ magnitudes versus our measured $R$ magnitudes for common galaxies. The SDSS completeness limit in the $R$-band is $\sim$18 mag. For galaxies with $R \leq 18$ mag, the RMS scatter is 0.22 mag. Relaxing the luminosity cut, the RMS scatter is 0.30 mag.
• Figure 5: The smoothed map of the flux scaling ratio (SR) variation across the observed field. The H$\alpha$+[N ii] flux and EW of each object are calculated using the scaling ratio for the corresponding location.
• Figure 6: The histogram of the $R$-band magnitudes of H$\alpha$ emitting members of the Coma cluster reported previously in the literature (black solid regions) and for those detected and confirmed Coma members in this survey (open histogram).