Spectroscopic characterization of the stellar content of ultra-diffuse galaxies

Abstract

Understanding the peculiar properties of Ultra Diffuse Galaxies (UDGs) via spectroscopic analysis is a challenging task requiring very deep observations and exquisite data reduction. In this work we perform one of the most complete characterisations of the stellar component of UDGs to date using deep optical spectroscopic data from OSIRIS at GTC. We measure radial and rotation velocities, star formation histories (SFH) and mean population parameters, such as ages and metallicities, for a sample of five UDG candidates in the Coma cluster. From the radial velocities, we confirm the Coma membership of these galaxies. We find that their rotation properties, if detected at all, are compatible with dwarf-like galaxies. The SFHs of the UDG are dominated by old (∼ 7 Gyr), metal-poor ([M/H] ∼ -1.1) and α-enhanced ([Mg/Fe] ∼ 0.4) populations followed by a smooth or episodic decline which halted ∼ 2 Gyr ago, possibly a sign of cluster-induced quenching. We find no obvious correlation between individual SFH shapes and any UDG morphological properties. The recovered stellar properties for UDGs are similar to those found for DDO 44, a local UDG analogue resolved into stars. We conclude that the UDGs in our sample are extended dwarfs whose properties are likely the outcome of both internal processes, such as bursty SFHs and/or high-spin haloes, as well as environmental effects within the Coma cluster.

Globular clusters in Coma cluster ultra-diffuse galaxies (UDGs): evidence for two types of UDG?

“…Only about a dozen higher surface brightness Coma UDGs have measured spectroscopic stellar population properties ( Ferré-Mateu et al (2018); Ruiz-Lara et al (2018); Gu et al (2018); Chilingarian et al (2019)). These studies generally found intermediate-to-old ages and low metallicities.…”

One Hundred SMUDGes in S-PLUS: Ultra-diffuse Galaxies Flourish in the Field

“…In Figure 8 we compare the luminosityweighted age distribution of galaxies in our sample to that of UDGs observed in the Coma (Gu et al 2018;Ruiz-Lara et al 2018;Ferré-Mateu et al 2018) and Virgo (Pandya et al 2018) clus- Considering that we only have luminosityweighted ages, the results from the our analysis are expected to be biased toward the youngest populations within a galaxy. Therefore, a few different, non-exclusive scenarios can explain the additional fraction of UDGs with young ages.…”

“…Prole et al 2019), are available for many UDGs but are of limited value in determining the properties of the stellar populations, while spectroscopy, which can provide the necessary information, is only available for a small number of galaxies (e.g. Martínez-Delgado et al 2016;Kadowaki et al 2017;Ruiz-Lara et al 2018;Ferré-Mateu et al 2018;Gu et al 2018).…”

“…Comparison of the luminosity-weighted ages of our UDGs, which are primarily in the field, and those of UDGs in the literature(Pandya et al 2018;Gu et al 2018;Ruiz-Lara et al 2018;Ferré- Mateu et al 2018), which are primarily in clusters.…”

A model for core formation in dark matter haloes and ultra-diffuse galaxies by outflow episodes

“…These Ultra Diffuse Galaxies (UDGs) appear to be ubiquitous in groups and clusters (e.g., van Dokkum et al 2015a,b;Janowiecki et al 2015;Koda et al 2015;Muñoz et al 2015;Mihos et al 2015Mihos et al , 2017Merritt et al 2016;van der Burg et al 2016;Yagi et al 2016;Janssens et al 2017;Shi et al 2017) but are also observed in the field (e.g., Román & Trujillo 2017;Leisman et al 2017). Spectroscopic studies of a few cases indicate intermediate to old, metal poor stellar populations for UDGs in groups and clusters (Ferré-Mateu et al 2018;Gu et al 2018;Ruiz-Lara et al 2018) while the spectral energy distribution (SED) fitting of a field UDG points towards younger stellar populations in the field (Pandya et al 2018). Possible formation scenarii include UDGs being (i) failed Milky Way-like galaxies that lost their gas after forming their first stars (van Dokkum et al 2015a(van Dokkum et al ,b, 2016Yozin & Bekki 2015;Peng & Lim 2016;Lim et al 2018), possibly due to the denser environment in groups and clusters, (ii) the highspin tail of the dwarf galaxy population (Amorisco & Loeb 2016;Rong et al 2017;Shi et al 2017), (iii) tidal debris from mergers or tidally disrupted dwarfs (Beasley & Trujillo 2016;Greco et al 2018;Jiang et al 2018) or (iv) galaxies whose spatial extend is due to episodes of inflows and outflows from stellar feedback (Di Cintio et al 2017).…”