Astronomy and Astrophysics – Astronomy
Scientific paper
Apr 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aj....137.3761b&link_type=abstract
The Astronomical Journal, Volume 137, Issue 4, pp. 3761-3777 (2009).
Astronomy and Astrophysics
Astronomy
8
Quasars: Absorption Lines, Quasars: Emission Lines, Quasars: General, Ultraviolet: Galaxies
Scientific paper
We present a sample of spectroscopically confirmed quasi-stellar objects (QSOs) with FUV-NUV color (as measured by Galaxy Evolution Explorer (GALEX) photometry, FUV band: 1344-1786 Å, NUV band: 1771-2831 Å) bluer than canonical QSO templates and than the majority of known QSOs. We analyze their FUV to NIR colors, luminosities, and optical spectra. The sample includes a group of 150 objects at low redshift (z < 0.5), and a group of 21 objects with redshift 1.7 < z < 2.6. For the low-redshift objects, the "blue" FUV-NUV color may be caused by enhanced Lyα emission, since Lyα transits the GALEX FUV band from z = 0.1 to z = 0.47. Synthetic QSO templates constructed with Lyα up to three times stronger than in standard templates match the observed UV colors of our low-redshift sample. Optical photometric and spectroscopic properties of these QSOs are not atypical. The Hα emission increases, and the optical spectra become bluer, with increasing absolute UV luminosity. The lack of selected objects at intermediate redshift is consistent with the fact that for z = 0.48-1.63, Lyα is included in the GALEX NUV band, making the observed FUV-NUV redder than the limit of our sample selection. The UV-blue QSOs at redshift ~2, where the GALEX bands sample rest-frame ≈450-590 Å (FUV) and ≈590-940 Å (NUV), are fainter than the average of UV-normal QSOs at similar redshift in NUV, while they have comparable luminosities in other bands. Therefore, we speculate that their observed FUV-NUV color may be explained by a combination of steep flux rise toward short wavelengths and dust absorption below the Lyman limit, such as from small grains or crystalline carbon (nanodiamonds). The ratio of Lyα to C IV could be measured in 10 objects; it is higher (30% on average) than for UV-normal QSOs, and close to the value expected for shock or collisional ionization. However, optical spectra are taken at different times than the UV photometry, which may bias the comparison if lines are variable. These QSO groups are uniquely set apart by the GALEX photometry within larger samples, given that their optical properties are not unusual.
Bianchi Luciana
Bressan Alessandro
Efremova Boryana
Herald James E.
Hutchings John B.
No associations
LandOfFree
Ultraviolet Quasi-Stellar Objects does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Ultraviolet Quasi-Stellar Objects, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ultraviolet Quasi-Stellar Objects will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1861143