Superluminous Spiral Galaxies

TL;DR

This paper reports the discovery of extremely luminous, massive spiral galaxies called super spirals, which challenge existing galaxy formation models and may represent a transitional evolutionary stage.

Contribution

It identifies and characterizes a new class of super luminous, massive spiral galaxies, expanding understanding of galaxy diversity and evolution.

Findings

53 super spirals identified out of 1616 SDSS galaxies

Super spirals have high star formation rates of 5-65 M_sun/yr

They are found in diverse environments, including mergers and cluster centers

Abstract

We report the discovery of spiral galaxies that are as optically luminous as elliptical brightest cluster galaxies, with r-band monochromatic luminosity L_r=8-14L* (4.3-7.5E44 erg/s). These super spiral galaxies are also giant and massive, with diameter D=57-134 kpc and stellar mass M_stars=0.3-3.4E11 M_sun. We find 53 super spirals out of a complete sample of 1616 SDSS galaxies with redshift z<0.3 and L_r>8L*. The closest example is found at z=0.089. We use existing photometry to estimate their stellar masses and star formation rates (SFRs). The SDSS and WISE colors are consistent with normal star-forming spirals on the blue sequence. However, the extreme masses and rapid SFRs of 5-65 M_sun/yr place super spirals in a sparsely populated region of parameter space, above the star-forming main sequence of disk galaxies. Super spirals occupy a diverse range of environments, from isolation to cluster centers. We find four super spiral galaxy systems that are late-stage major mergers--a possible clue to their formation. We suggest that super spirals are a remnant population of unquenched, massive disk galaxies. They may eventually become massive lenticular galaxies after they are cut off from their gas supply and their disks fade.