NGC 404: A REJUVENATED LENTICULAR GALAXY ON A MERGER-INDUCED, BLUEWARD EXCURSION INTO THE GREEN VALLEY

Journal Article · Sat May 01 00:00:00 EDT 2010 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/714/1/L171· OSTI ID:21448922

Thilker, David A; Bianchi, Luciana ^[1]; Schiminovich, David ^[2]; Gil de Paz, Armando ^[3]; Seibert, Mark; Madore, Barry F ^[4]; Wyder, Ted; Barlow, Tom; Conrow, Tim; Forster, Karl; Friedman, Peter; Martin, Chris; Morrissey, Patrick; Small, Todd ^[5]; Rich, R Michael ^[6]; Yi, Sukyoung ^[7]; Neff, Susan ^[8]

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1. Center for Astrophysical Sciences, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218 (United States)
2. Department of Astronomy, Columbia University, 550 West 120th Street, New York, NY 10027 (United States)
3. Departamento de AstrofIsica y CC. de la Atmosfera, Universidad Complutense de Madrid, Avda. de la Complutense, s/n, E-28040 Madrid (Spain)
4. Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101 (United States)
5. California Institute of Technology, MC 405-47, 1200 East California Boulevard, Pasadena, CA 91125 (United States)
6. Department of Physics and Astronomy, UCLA, Los Angeles, CA 90095-1547 (United States)
7. Department of Astronomy, Yonsei University, Seoul 120-749 (Korea, Republic of)
8. Laboratory for Astronomy and Solar Physics, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

We have discovered recent star formation in the outermost portion ((1-4) x R {sub 25}) of the nearby lenticular (S0) galaxy NGC 404 using Galaxy Evolution Explorer UV imaging. FUV-bright sources are strongly concentrated within the galaxy's H I ring (formed by a merger event according to del RIo et al.), even though the average gas density is dynamically subcritical. Archival Hubble Space Telescope imaging reveals resolved upper main-sequence stars and conclusively demonstrates that the UV light originates from recent star formation activity. We present FUV, NUV radial surface brightness profiles, and integrated magnitudes for NGC 404. Within the ring, the average star formation rate (SFR) surface density ({Sigma}{sub SFR}) is {approx}2.2 x 10{sup -5} M {sub sun} yr{sup -1} kpc{sup -2}. Of the total FUV flux, 70% comes from the H I ring which is forming stars at a rate of 2.5 x 10{sup -3} M {sub sun} yr{sup -1}. The gas consumption timescale, assuming a constant SFR and no gas recycling, is several times the age of the universe. In the context of the UV-optical galaxy color-magnitude diagram, the presence of the star-forming H I ring places NGC 404 in the green valley separating the red and blue sequences. The rejuvenated lenticular galaxy has experienced a merger-induced, disk-building excursion away from the red sequence toward bluer colors, where it may evolve quiescently or (if appropriately triggered) experience a burst capable of placing it on the blue/star-forming sequence for up to {approx}1 Gyr. The green valley galaxy population is heterogeneous, with most systems transitioning from blue to red but others evolving in the opposite sense due to acquisition of fresh gas through various channels.

• OSTI ID: 21448922
• Journal Information: Astrophysical Journal Letters, Vol. 714, Issue 1; Other Information: DOI: 10.1088/2041-8205/714/1/L171; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
BRIGHTNESS
COLOR
GALACTIC EVOLUTION
GALAXIES
MAIN SEQUENCE STARS
TELESCOPES
ULTRAVIOLET RADIATION
UNIVERSE
ELECTROMAGNETIC RADIATION
EVOLUTION
OPTICAL PROPERTIES
ORGANOLEPTIC PROPERTIES
PHYSICAL PROPERTIES
RADIATIONS
STARS