CANDELS: THE CORRELATION BETWEEN GALAXY MORPHOLOGY AND STAR FORMATION ACTIVITY ATz∼ 2

Abstract

We discuss the state of the assembly of the Hubble Sequence in the mix of bright galaxies at redshift 1.4 < z ≤ 2.5 with a large sample of 1,671 galaxies down to H AB ∼ 26, selected from the HST/ACS and WFC3 images of the GOODS-South field obtained as part of the GOODS and CANDELS observations. We investigate the relationship between the star formation properties and morphology using various parametric diagnostics, such as the Sérsic light profile, Gini (G), M 20 , Concentration (C), Asymmetry (A) and multiplicity (Ψ) parameters. Our sample clearly separates into massive, red and passive galaxies versus less massive, blue and star forming ones, and this dichotomy correlates very well with the galaxies' morphological properties. Star-forming galaxies show a broad variety of morphological features, including clumpy structures and bulges mixed with faint low surface brightness features, generally characterized by disky-type light profiles. Passively evolving galaxies, on the other hand, very often have compact light distribution and morphology typical of today's spheroidal systems. We also find that artificially redshifted local galaxies have a similar distribution with z ∼ 2 galaxies in a G-M 20 plane. Visual inspection between the rest-frame optical and UV images show that there is a generally weak morphological k-correction for galaxies at z ∼ 2, but the comparison with non-parametric measures show that galaxies in the rest-frame UV are somewhat clumpier than rest-frame optical. Similar general trends are observed in the local universe among massive galaxies, suggesting that the backbone of the Hubble sequence was already in place at z ∼ 2.

The host galaxies of X-ray selected active galactic nuclei toz= 2.5: Structure, star formation, and their relationships from CANDELS andHerschel/PACS

“…This is as expected -most of the SF in the local Universe and at higher redshifts is associated with galaxies having substantial disks (e.g., Kauffmann et al 2003;Wuyts et al 2011;Lee et al 2013), although at z ∼ 2, a sizeable population of blue star-forming compact spheroids is also found (Barro et al 2013). In contrast to the inactive galaxies, the AGNs show a much flatter dependence of mean L 60 with n, such that low Sérsic galaxies and AGNs have comparable FIR luminosities, but, especially at z < 1.5, high Sérsic AGNs are significantly more luminous than high Sérsic galaxies.…”

The Lyman alpha reference sample

“…13 shows that z2LARS have morphology consistent with that of merging system, like z ∼ 2.5 SMGs and some of the LBGs studied by Lotz et al (2004). They tend to be separated from the location of z ∼ 2 sBzK and pBzK galaxies (Lee et al 2013). Some z2LARS-LAEs show a larger G rP20 per M20 value than the other z2LARS.…”

“…First of all the rest-frame UV morphology is sensitive to the current star formation; the rest-frame optical traces the structure of the entire galaxy stellar population (Lee et al 2013;Bond et al 2014). The combinations of parameters (see previous section) we adopted are, -Asymmetry vs. concentration, asymmetry vs. clumpiness, together with clumpiness vs. concentration, as presented by Conselice (2003) -Gini coefficient vs. M20 bright-pixel moment, as presented in Lotz et al (2004).…”

“…These authors have pointed out that, based on their number densities, masses, sizes, and star formation rates, z ∼ 2−3 compact, star-forming galaxies were likely progenitors of compact, quiescent, massive galaxies at z < 2. -Star-forming galaxies selected based on their B − z and z − K colour (sBzK, Yuma et al 2012;Lee et al 2013); passive and star-forming galaxies selected based on their B − z and z − K colour (pBzK and sBzK, Lee et al 2013). -Star-forming galaxies at z ∼ 2−3 by Law et al (2012).…”

“…In the sample of LARS galaxies, 70% show a Spearman probability p ∼ 0.0 and coefficient r ∼ −1 for the correlation of ellipticity. (Lee et al 2013, grey diamonds and yellow squares), and z ∼ 2.5 SMGs (Aguirre et al 2013, black circles), where the measurements are all performed on HST images. The dashed line indicates the separation between normal galaxies and merging systems by Lotz et al (2008).…”