A redshift survey of the nearby galaxy cluster Abell 2199 : No upturn of the faint-end slope of galaxy luminosity function

TL;DR

This study measures the galaxy luminosity function in Abell 2199 down to $M_r \sim -14.5$ using a deep, spectroscopically complete sample built from MMT/Hectospec and DESI DR1 data, supplemented by SDSS. The LF is well described by a Schechter function with $M^* = -21.30 \pm 0.27$ and $\alpha = -1.23 \pm 0.05$, showing no evidence for a steep faint-end upturn ($\alpha \sim -2$) in the cluster core. Comparisons with Coma, Virgo, local field samples, and the TNG50-1 simulation yield consistent, relatively shallow faint-end slopes, suggesting environmental processes in dense cluster cores do not enhance the survival or formation of low-mass galaxies. The results argue against a universal, cluster-driven upturn in the faint-end of the galaxy LF and highlight the importance of spectroscopic completeness to avoid background contamination in such measurements.

Abstract

We determine the galaxy luminosity function of cluster galaxies in the nearby galaxy cluster Abell 2199 (A2199), focusing on the faint-end slope down to $M_r \sim -14.5$. To achieve this, we augment the existing dataset by adding redshift data from our deep MMT/Hectospec survey and from the Dark Energy Spectroscopic Instrument (DESI), significantly improving the spectroscopic completeness down to $r_{\mathrm{petro},0} = 20.8$ within the central $30^\prime$ region. The resulting luminosity function is well described by a Schechter function with a characteristic magnitude $M^* = -21.30 \pm 0.27$ and a faint-end slope $α= -1.23 \pm 0.05$. This faint-end slope is consistent with those measured in the nearby Coma and Virgo clusters and in a cluster from the TNG50 cosmological simulation, and is slightly shallower than that of field galaxies. These findings indicate that the previously claimed steep faint-end upturn (with $α\sim -2$) in nearby galaxy clusters is not supported. Instead, they indicate that environmental processes in dense cluster cores does not seem to trigger the formation or survival of low-mass galaxies, thereby preventing a steep faint-end upturn in the luminosity function.

Figures (7)

• Figure 1: (a) (Top) Histogram of galaxies within 30$^\prime$ from the cluster center for all galaxies with spectroscopy, shown as a function of $r$-band Petrosian magnitude. The black dashed and red solid lines show the results before and after this study, respectively. (Bottom) Differential spectroscopic completeness, $f_\mathrm{spec}$, as a function of magnitude. The black and red dotted lines indicate the magnitude limits where the spectroscopic completeness falls below 50%, before and after this study, respectively. (b) Spatial spectroscopic completeness of galaxies with $m_{r,\mathrm{Petro},0} < 20.5$ in the A2199 field. Marginal spectroscopic completeness along the spatial axes—right ascension (top) and declination (right)—is shown in the subpanels. Darker colors indicate higher spatial spectroscopic completeness. White circles show the member galaxies, whose density distribution is indicated by white contours. Red and orange circles indicate the $R_{500}$ and $R_{200}$ of A2199, respectively.
• Figure 2: (Top) Distribution of $m_{r,\mathrm{Petro},0}$ as a function of redshift. Red dots indicate the galaxies with redshifts from this study. (Bottom) Redshift histogram of galaxies. The black histogram shows all galaxies in the sample. The blue histogram shows the distribution of member galaxies. Red histogram shows the redshifts from this study.
• Figure 3: $(g-r)_\mathrm{model}$ color vs. $m_{r,\mathrm{Petro},0}$ magnitude diagram of galaxies within $30^\prime$ of the A2199 cluster center. Gray dots show galaxies without spectroscopic redshifts. Green squares indicate galaxies with spectroscopic redshifts. Red circles are red sequence member galaxies and the blue crosses are blue member galaxies. The member galaxies are spectroscopically confirmed. The black solid line shows the red sequence of A2199 members in this study. The black dotted line shows the red sequence of A2199 members from Song2017. The blue dashed line shows the red sequence of Perseus members from Kang2024. The orange dot-dashed line shows the red sequence of Coma members from Kang2025. Red shade shows the range of red sequence of the MACH clusters at $0.07<z<0.11$ (Park in prep.)
• Figure 4: (Middle left) Rest-frame cluster-centric velocities of galaxies as a function of projected cluster-centric radius. The caustic profile of A2199 is shown as a black solid line. Red circles and blue crosses indicate red and blue member galaxies, respectively. Black dots represent non-member galaxies. (Middle right) Histograms of rest-frame cluster-centric velocities for galaxies with redshifts in the A2199 field. Red and blue hatched histograms correspond to red and blue member galaxies, respectively. The black solid-line histogram includes all the number of galaxies with measured redshifts in the field. (Top) Histograms of the radial distribution of red and blue member galaxies as a function of cluster-centric distance. (Bottom left) Apparent $r$-band Petrosian magnitude ($m_{r,\mathrm{Petro},0}$) versus projected cluster-centric distance. Black dots indicate non-member galaxies with measured redshifts (Bottom right) Histogram of $m_{r,\mathrm{Petro},0}$. The purple histogram shows all spectroscopically confirmed member galaxies in A2199, while the black histogram shows all non-member galaxies with measured redshifts within the A2199 field.
• Figure 5: Luminosity function of A2199. The black triangles represent the raw luminosity function. The red circles indicate the luminosity function corrected for data incompleteness. Error bars represent Poisson errors. The red dashed line shows the Schechter function fit. The gray shaded region indicates the magnitude range where the spectroscopic completeness is below $f_\mathrm{spec} < 0.5$.