TY - JOUR
T1 - NGC 404
T2 - A rejuvenated lenticular galaxy on a merger-induced, blueward excursion into the green valley
AU - Thilker, David A.
AU - Bianchi, Luciana
AU - Schiminovich, David
AU - Gil De Paz, Armando
AU - Seibert, Mark
AU - Madore, Barry F.
AU - Wyder, Ted
AU - Rich, R. Michael
AU - Yi, Sukyoung
AU - Barlow, Tom
AU - Conrow, Tim
AU - Forster, Karl
AU - Friedman, Peter
AU - Martin, Chris
AU - Morrissey, Patrick
AU - Neff, Susan
AU - Small, Todd
PY - 2010
Y1 - 2010
N2 - 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 etal.), 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 (ΣSFR) is 2.2 × 10-5 Myr-1kpc-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.
AB - 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 etal.), 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 (ΣSFR) is 2.2 × 10-5 Myr-1kpc-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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U2 - 10.1088/2041-8205/714/1/L171
DO - 10.1088/2041-8205/714/1/L171
M3 - Article
AN - SCOPUS:77950930291
SN - 2041-8205
VL - 714
SP - L171-L175
JO - Astrophysical Journal Letters
JF - Astrophysical Journal Letters
IS - 1 PART 2
ER -