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NGC 404: a rejuvenated lenticular galaxy on a Merger-induced, blueward excursion into the Green Valley

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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 2041-8205

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Official URL: http://dx.doi.org/10.1088/2041-8205/714/1/L171


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http://iopscience.iop.org/Publisher


Abstract

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.


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© 2010. The American Astronomical Society.
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).

Uncontrolled Keywords:Color-magnitude diagram; Star-formation rates; Red sequence; Stellar populations; Neutral hydrogen; Local universe; Molecular gas; Formation law; Ionized-gas; HI survey
Subjects:Sciences > Physics
Sciences > Physics > Astrophysics
Sciences > Physics > Astronomy
ID Code:35495
Deposited On:03 Feb 2016 15:33
Last Modified:10 Dec 2018 15:05

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