Linking compact dwarf starburst galaxies in the RESOLVE survey to downsized blue nuggets

Abstract

We identify and characterize compact dwarf starburst (CDS) galaxies in the RE-SOLVE survey, a volume-limited census of galaxies in the local universe, to probe whether this population contains any residual "blue nuggets," a class of intensely starforming compact galaxies first identified at high redshift z. Our 50 low-z CDS galaxies are defined by dwarf masses (stellar mass M * < 10 9.5 M ), compact bulged-disk or spheroid-dominated morphologies (using a quantitative criterion, µ ∆ > 8.6), and specific star formation rates above the defining threshold for high-z blue nuggets (log SSFR [Gyr −1 ] > −0.5). Across redshifts, blue nuggets exhibit three defining properties: compactness relative to contemporaneous galaxies, abundant cold gas, and formation via compaction in mergers or colliding streams. Those with halo mass below M halo ∼ 10 11.5 M may in theory evade permanent quenching and cyclically refuel until the present day. Selected only for compactness and starburst activity, our CDS galaxies generally have M halo 10 11.5 M and gas-to-stellar mass ratio 1. Moreover, analysis of archival DECaLS photometry and new 3D spectroscopic observations for CDS galaxies reveals a high rate of photometric and kinematic disturbances suggestive of dwarf mergers. The SSFRs, surface mass densities, and number counts of CDS galaxies are compatible with theoretical and observational expectations for redshift evolution in blue nuggets. We argue that CDS galaxies represent a maximally-starbursting subset of traditional compact dwarf classes such as blue compact dwarfs and blue E/S0s. We conclude that CDS galaxies represent a low-z tail of the blue nugget phenomenon formed via a moderated compaction channel that leaves open the possibility of disk regrowth and evolution into normal disk galaxies.

Identification and Quenching of Nugget Galaxies in the RESOLVE Survey at z = 0

“…The 28 remaining CDS galaxies from Palumbo et al (2020) are either satellites/flybys or not compact enough to be in our final nugget sample. Similarly, 21 out of our 52 dwarf HSF nugget candidates are CDS galaxies in Palumbo et al (2020). The other 31 dwarf HSF nugget candidates excluded from Palumbo et al (2020) did not pass their starbursting criterion and/or morphology criterion (which selects on a parameter akin to Hubble type; see Kannappan et al 2013).…”

“…Additionally, these samples do not extend below the threshold scale, where cyclic quenching is predicted. Palumbo et al (2020) were the first to find that compact dwarf starburst (CDS) galaxies exist within the cyclic quenching regime at z ∼ 0 and some of these CDS galaxies are likely low-z blue nugget analogs, but they selected highly starforming galaxies, thereby excluding quenching and quenched systems.…”

“…In this paper, we construct the first complete census of nuggets at all evolutionary stages within the volume-and masslimited z ∼ 0 REsolved Spectroscopy Of a Local VolumE (RESOLVE) survey (Kannappan & Wei 2008), the same survey used by Palumbo et al (2020). Creating this census will allow us to answer the key question: Do real nuggets show evidence of cyclic quenching below the threshold scale and permanent quenching above the threshold scale, as predicted by theory?…”

Design of a Skipper CCD focal plane for the SOAR integral field spectrograph

“…Furthermore, SIFS uses volume phase holographic (VPH) transmission gratings that offer a range of spectral resolution (R = δλ/λ) from 5000 < R < 30000, which is sufficient to measure stellar metallicities at R > 6000 and abundance ratios, such as Hα/Fe, at R > 15000 [1,3,13]. For example, Palumbo et al (2020) used SIFS to measure redshifts, velocity fields, which were constructed by sampling object spectra at many discrete points, specific start formation rates, and surface mass densities of compact dwarf starburst galaxies in the Local Volume [14]. Patrícia da Silva at al.…”

“…We will follow the procedure described in Greco et al (2018) [26] to select likely star-forming LSBGs starting with the blue subpopulation and matching to UV detections in GALEX. We will then use the procedure described in Palumbo et al (2020) [14] to extract object's physical properties from SIFS data cubes after having selected target LSBGs. Our goal is to demonstrate that the AstroSkipper will reduce readout noise in the detector pixels corresponding to the expected spatial and spectral location of star-forming H ii regions in the targeted LSBGs.…”