ID-MAGE II: The Star Forming Satellites of Low-Mass Hosts

Abstract

We present results from our ongoing campaign to follow up the satellite candidates from the Identifying Dwarfs of MC Analog GalaxiEs (ID-MAGE) survey. Previously, we published a list of 355 unresolved satellite candidates identified around 36~nearby LMC- and SMC-mass hosts (D$=$4$-$10~Mpc). We present the velocities of 83 satellite candidates from new Green Bank Telescope \hi\ observations, optical long-slit spectra, and the Dark Energy Survey Instrument Data Release 1. Based on their velocities, we identify six candidates as probable satellite galaxies ($6.5\times10^5\leq M_\star/M_\odot\leq1.5\times10^7$) and 77 as background galaxies. Our results underscore the ability of spectroscopic follow-up to effectively separate satellites from background galaxies. Using the refined sample, we update our previously derived estimates for the average satellite population per host and find 1.7$\pm$0.7 (1.0$\pm$0.3) satellites per LMC-mass (SMC-mass) host. Our current satellite sample includes 25 galaxies confirmed by distances or velocities. This set includes the complete satellite populations of three hosts (UGC~04422: zero satellites, UGC~08201: zero satellites, NGC~3432: four satellites), which we compare to simulations and known satellite systems from the literature. Our sample is nearly complete for the most massive satellites (M$_\star > 10^7~M_\odot$). We find these massive satellites have a quenched fraction of 10--25\%, placing them between the $<$5\% quenched fraction of isolated galaxies and the 40--70\% quenched fraction of MW-analog satellites with $10^7~M_\odot < $ M$_\star < 10^8~M_\odot$. This demonstrates the impact that low-mass galaxies have on the evolution of their satellites.

Figures (11)

• Figure 1: The plot shows the candidates' relative velocities ($v_r$) versus their projected radial distances. The blue circles are the candidates with velocities in agreement with their hosts while red crosses are background galaxies based on $v_r$. A limit of $|v_r|\leq$150 km s$^{-1}$ (horizontal dashed lines) is used as the threshold for confirmation. The limit of our surveyed area (150 kpc) is shown with a vertical dashed line. The black and gray lines are the escape velocity curves for LMC-mass ($1.8\times10^{11}M_\odot$) and SMC-mass ($9.5\times10^{10}M_\odot$) point masses from the Brook14 model used in Dooley17.
• Figure 2: Compare to Figure 7 in idmage: The central concentration of our probable and confirmed satellites and high-likelihood sample candidates: the number of galaxies per equal-area annular bin per host as a function of projected radius (excluding NGC 3738). Left panel: The sample for all hosts. Center panel: The sample for LMC-mass hosts. Right: The sample for SMC-mass hosts. Error bars represent the Poisson uncertainties per bin. The projected distance to each satellite is based on the known distance of its assumed host. This equal-area binning highlights the concentration of galaxies within $\sim60$ kpc of their hosts.
• Figure 3: The total number of satellites based on the probable and confirmed satellites around the ID-MAGE hosts NGC 3432, UGC 04426, and UGC 08201 (x's) in comparison to the Dooley17 (shaded orange) model predictions of number of satellites per host stellar mass. The confirmed satellites identified in Carlin21Carlin24KimYJ2022ADD3109ELVES-DwarfLiddo161Medoff25stierwalt25 are included for comparison. For the LMC, a lower limit is used as its satellite population is uncertain due to the gravitational influence of the MW (e.g., Pardy20Patel20. The uncertainties in DDO 161's stellar mass are shown because they are significantly larger than the mass uncertainties for the other hosts. Due to observational limits, the satellite counts shown are lower bounds for most hosts.
• Figure 4: The satellite mass function for the LMC-mass host NGC 3432 in comparison to the Dooley17 (shaped green) and Santos-Santos22 (shaded red) model predictions. The dashed vertical line is the ID-MAGE completeness limit for NGC 3432. The mass function for NGC 3432 is $3\sigma$ outlier above the Dooley17 predictions and $1.5\sigma$ above Santos-Santos22's predictions.
• Figure 5: GBT H i spectrum of MAGE J0006-2456 taken as part of project ID GBT25A-155. The H i emission line used to derive the velocity (570$\pm$2km s$^{-1}$) is marked.