Thilker, David A. and Bianchi, Luciana and Schiminovich, David and Gil de Paz, Armando and Seibert, Mark and Madore, Barry F. and Wyder, Ted and Rich, R. Michael and Yi, Sukyoung and Barlow, Tom and Conrow, Tim and Forster, Karl and Friedman, Peter and Martin, Chris and Morrissey, Patrick and Neff, Susan and Small, Todd (2010) NGC 404: A Rejuvenated Lenticular Galaxy on a Merger-induced, Blueward Excursion Into the Green Valley. Astrophysical Journal Letters, 714 (1). L171-L175. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:20100525-113912244
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We have discovered recent star formation in the outermost portion ((1-4) × R_(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 Río 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 (Σ_(SFR)) is ~2.2 × 10^(–5) M_☉ yr^(–1) kpc^(–2). Of the total FUV flux, 70% comes from the H I ring which is forming stars at a rate of 2.5 × 10^(–3) M_☉ yr^(–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 ~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.
|Additional Information:||© 2010 American Astronomical Society. Received 2009 October 6; accepted 2010 March 24; published 2010 April 9. GALEX is a NASA Small Explorer, launched in 2003 April. We gratefully acknowledge NASA’s support for construction, operation, and science analysis for the GALEX mission, developed in cooperation with the Centre National d’Etudes Spatiales of France and the Korean Ministry of Science and Technology. This research has made use of the NASA/IPAC Extragalactic Database (NED). We acknowledge the usage of the HyperLeda database (http://leda.univ-lyon1.fr). The Digitized Sky Surveys were produced at the Space Telescope Science Institute under U.S. Government grant NAG W-2166. Some images presented in this Letter were obtained from the Multimission Archive at the Space Telescope Science Institute (MAST). Facilities: GALEX, HST (WFPC2), VLA, WSRT|
|Group:||Space Radiation Laboratory|
|Subject Keywords:||galaxies: elliptical and lenticular, cD; galaxies: evolution; galaxies: individual (NGC 404); galaxies: interactions; galaxies: structure|
|Classification Code:||PACS: 98.52.Lp; 95.85.Ls; 98.58.Ge; 98.62.Lv; 98.62.Ai; 98.62.Qz|
|Official Citation:||David A. Thilker et al 2010 ApJ 714 L171 doi: 10.1088/2041-8205/714/1/L171|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Jason Perez|
|Deposited On:||25 May 2010 20:13|
|Last Modified:||04 Mar 2013 18:01|
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