Clumpy Galaxies in Goods and Gems: Massive Analogs of Local Dwarf Irregulars

Abstract

Clumpy galaxies in the Galaxy Evolution from Morphology and SEDs and Great Observatories Origins Deep Survey fields are examined for clues to their evolution into modern spirals. The magnitudes of the clumps and the surface brightnesses of the interclump regions are measured and fitted to models of stellar age and mass. There is an evolutionary trend from clump clusters with no evident interclump emission to clump clusters with faint red disks, to spiral galaxies of the flocculent or grand design types. Along this sequence, the interclump surface density increases and the mass surface density contrast between the clumps and the interclump regions decreases, suggesting a gradual dispersal of clumps to form disks. Also along this sequence, the bulge-to-clump mass ratios and age ratios increase, suggesting a gradual formation of bulges. All of these morphological types occur in the same redshift range, indicating that the clump cluster morphology is not the result of bandshifting. This redshift range also includes clear examples of interacting galaxies with tidal tails and other characteristic features, indicating that clump clusters, which do not have these features, are not generally interacting. Comparisons to local galaxies with the same rest wavelength and spatial resolution show that clump clusters are unlike local flocculent and spiral galaxies primarily because of the high clump/interclump contrasts in the clump clusters. They bear a striking resemblance to local dwarf irregulars, however. This resemblance is consistent with a model in which the clumpy morphology comes from gravitational instabilities in gas with a high turbulent speed compared to the rotation speed and a high mass fraction compared to the stars. The morphology does not depend on galaxy mass as much as it depends on evolutionary stage: clump clusters are 100 times more massive than local dwarfs. The apparent lack of star formation in damped Lyman alpha absorbers may result from fast turbulence.

Integral-field near-infrared spectroscopy of two blue dwarf galaxies: NGC 5253 and He 2-10

“…Cresci et al 2009;Epinat et al 2009;Law et al 2009). Because the Jeans length L J in a gas rich system is proportional to (σ/V) 2 (Genzel et al 2008), this supports the idea that the clumpy morphology of both high redshift disks and blue dwarf galaxies comes from gravitational instabilities in gas with high turbulent speed compared to the rotation speed, and a high mass fraction compared to the stars (see Elmegreen et al 2009). …”

“…These clusters could be the progenitors of the old globular clusters observed in most galaxies today (de Grijs & Parmentier 2007), thus providing further evidence for the link between the starburst phenomenon and the formation of galaxies. Moreover, star-forming regions with properties consistent with the more massive HII regions detected locally are observed up to z ∼ 5 (Swinbank et al 2009), and local dwarf galaxies have been identified as scaled down analogs of clumpy starforming galaxies at high redshift (Elmegreen et al 2009). Dwarf for He 2-10, the clusters (L1-6) from Cabanac et al (2005) and the radio knots (knot 1-5) from Kobulnicky & Johnson (1999) are marked, while for NGC 5253 the clusters from Calzetti et al (1997) and Vanzi & Sauvage (2004).…”

The age structure of stellar populations in the solar vicinity

“…With the higher dispersions necessary to keep the disk near the line of stability suggests that the disks are generally thicker than disks in the local universe as perhaps observed (e.g. Elmegreen et al 2009;Epinat et al 2012). …”

Star formation sustained by gas accretion

“…Glazebrook et al 1995;Abraham et al 1996a,b;van den Bergh et al 1996;Cowie et al 1995;Im et al 1999;Elmegreen et al 2004Elmegreen et al , 2005Elmegreen et al , 2007bElmegreen et al , 2009Förster Schreiber et al 2009 with large SFR in excess of 100 M year −1 (e.g. Bauer et al 2011).…”