Local Compact Galaxies Research Articles

Modeling ALMA Observations of the Warped Molecular Gas Disk in the Red Nugget Relic Galaxy NGC 384

We present 0.″22 resolution CO(2–1) observations of the circumnuclear gas disk in the local compact galaxy NGC 384 with the Atacama Large Millimeter/submillimeter Array (ALMA). While the majority of the disk displays regular rotation with projected velocities rising to 370 km s−1, the inner ∼0.″5 exhibits a kinematic twist. We develop warped disk gas-dynamical models to account for this twist, fit those models to the ALMA data cube, and find a stellar mass-to-light ratio in the H band of M/L H = 1.34 ± 0.01 [1σ statistical] ±0.02 [systematic] M ⊙/L ⊙ and a supermassive black hole (BH) mass (M BH) of M BH =(7.26−0.48+0.43[1σstatistical]−1.00+0.55[systematic])×108M⊙ . In contrast to most previous dynamical M BH measurements in local compact galaxies, which typically found over-massive BHs compared to the local BH mass−bulge luminosity and BH mass−bulge mass relations, NGC 384 lies within the scatter of those scaling relations. NGC 384 and other local compact galaxies are likely relics of z ∼ 2 red nuggets, and over-massive BHs in these relics indicate BH growth may conclude before the host galaxy stars have finished assembly. Our NGC 384 results may challenge this evolutionary picture, suggesting there may be increased scatter in the scaling relations than previously thought. However, this scatter could be inflated by systematic differences between stellar- and gas-dynamical measurement methods, motivating direct comparisons between the methods for NGC 384 and the other compact galaxies in the sample.

КОМПАКТНІ ГАЛАКТИКИ З АКТИВНИМ ЗОРЕУТВОРЕННЯМ: СТАТИСТИЧНІ ВЛАСТИВОСТІ ПІДВИБІРОК ІЗ ПОРОГОВИМ ЗНАЧЕННЯМ ПОТОКУ ВИПРОМІНЮВАННЯ У ЛІНІЇ Hβ

We study the dependence of the luminosity of starburst galaxy on the young age (< 10 Myr) of star formation burst and metallicity. We also study the luminosity function (LF) for different subsamples of starburst galaxies. These subsamples with different threshold values of the Hβ emission line fluxes were formed from a sample of 14,000 local compact galaxies with active star formation. We obtain relations for a temporal evolution of luminosity-to-stellar mass of young stellar population ratio on the starburst age and metallicity. Luminosity functions for subsamples of galaxies with Hβ fluxes exceeding a certain threshold value are shown to differ from Schechter’s LF at the high luminosity end. They are adequately described by a log-normal function with parameters determined by the maximum likelihood method. The results confirm and complement the conclusions made in previous studies of the starburst galaxy samples.

THE EVOLUTION OF THE NUMBER DENSITY OF COMPACT GALAXIES

We compare the number density of compact (small size) massive galaxies at low and high redshift using our Padova Millennium Galaxy and Group Catalogue (PM2GC) at z=0.03-0.11 and the CANDELS results from Barro et al. (2013) at z=1-2. The number density of local compact galaxies with luminosity weighted (LW) ages compatible with being already passive at high redshift is compared with the density of compact passive galaxies observed at high-z. Our results place an upper limit of a factor ~2 to the evolution of the number density and are inconsistent with a significant size evolution for most of the compact galaxies observed at high-z. The evolution may be instead significant (up to a factor 5) for the most extreme, ultracompact galaxies. Considering all compact galaxies, regardless of LW age and star formation activity, a minority of local compact galaxies (<=1/3) might have formed at z<1. Finally, we show that the secular decrease of the galaxy stellar mass due to simple stellar evolution may in some cases be a non-negligible factor in the context of the evolution of the mass-size relation, and we caution that passive evolution in mass should be taken into account when comparing samples at different redshifts.

The Nature of Compact Galaxies in the Hubble Deep Field. II. Spectroscopic Properties and Implications for the Evolution of the Star Formation Rate Density of the Universe

We present a spectroscopic study of 51 compact field galaxies with redshifts z 0.7 have similar SFRs per unit mass to those at z<0.7, they are on average 10 times more massive. Our sample implies a lower limit for the global comoving SFR density of 0.004 M yr^-1 Mpc^-3 at z = 0.55, and 0.008 M yr^-1 Mpc^-3 at z = 0.85 (assuming Salpeter IMF, Ho = 50 km s^-1 Mpc^-1, and qo = 0.5). These values, when compared to estimates for a sample of local compact galaxies selected in a similar fashion, support a history of the universe in which the SFR density declines by a factor 10 from z = 1 to today.