arXiv subjects
Publications and source records attributed to Sylvain Veilleux.
A review of the spectroscopic tools needed to characterize AGNs is presented. This review focusses on ultraviolet, optical and infrared emission-line diagnostics specifically designed to help differentiate AGNs from starburst-dominated galaxies. The strengths and weaknesses of these methods are discussed in the context of on-going and future AGN surveys.
Multi-line imaging of the nearby disk galaxy NGC 1482 with the Taurus Tunable Filter (TTF) on the Anglo-Australian Telescope reveals a remarkable hourglass-shaped [N II] 6583/H-alpha excitation structure suggestive of a galactic wind extending at least 1.5 kpc above and below the disk of the host galaxy. Long-slit spectroscopy confirms the existence of a large-scale outflow in this galaxy. The entrained wind material has [N II] 6583/H-alpha ratios in excess of unity while the disk material is characterized by H II region-like line ratios indicative of a starburst. Expansion velocities of order 250 km/s are detected in the wind material, and a lower limit of 2 x 10^{53} ergs is derived for the kinetic energy of the outflow based on the gas kinematics and the amount of ionized material entrained in the outflow. This is the first time to our knowledge that a galactic wind is discovered using excitation maps. This line ratio technique represents a promising new way to identify wind galaxy candidates before undergoing more time-consuming spectroscopic follow-ups. This method of selection may be particularly useful for samples of galaxies at moderate redshifts.
We present photometric observations of an apparent Type Ia supernova (SN Ia) at a redshift of ~1.7, the farthest SN observed to date. SN 1997ff, was discovered in a repeat observation by the HST of the HDF-), and serendipitously monitored with NICMOS on HST throughout the GTO campaign. The SN type can be determined from the host galaxy type:an evolved, red elliptical lacking enough recent star formation to provide a significant population of core-collapse SNe. The class- ification is further supported by diagnostics available from the observed colors and temporal behavior of the SN, both of which match a typical SN Ia. The photo- metric record of the SN includes a dozen flux measurements in the I, J, and H bands spanning 35 days in the observed frame. The redshift derived from the SN photometry, z=1.7+/-0.1, is in excellent agreement with the redshift estimate of z=1.65+/-0.15 derived from the U_300,B_450,V_606,I_814,J_110,J_125,H_160, H_165,K_s photometry of the galaxy. Optical and near-infrared spectra of the host provide a very tentative spectroscopic redshift of 1.755. Fits to observations of the SN provide constraints for the redshift-distance relation of SNe~Ia and a powerful test of the current accelerating Universe hypothesis. The apparent SN brightness is consistent with that expected in the decelerating phase of the preferred cosmological model, Omega_M~1/3, Omega_Lambda~2/3. It is inconsistent with grey dust or simple luminosity evolution, candidate astro- physical effects which could mimic past evidence for an accelerating Universe from SNe Ia at z~0.5.We consider several sources of possible systematic error including lensing, SN misclassification, selection bias, and calibration errors. Currently, none of these effects appears likely to challenge our conclusions.
The issue of a starburst-AGN connection in local and distant galaxies is relevant for understanding galaxy formation and evolution, the star formation and metal enrichment history of the universe, the origin of the extragalactic background at low and high energies, and the origin of nuclear activity in galaxies. Here I review some of the observational evidence recently brought forward in favor of a connection between the starburst and AGN phenomena. I conclude by raising a number of questions concerning the exact nature of this connection.
We present ROSAT PSPC and HRI images of eight galaxies selected from a distance-limited sample of 22 edge-on Seyfert galaxies. Kiloparsec-scale soft X-ray nebulae extend along the galaxy minor axes in three galaxies (NGC 2992, NGC 4388 and NGC 5506). The extended X-ray emission has 0.2-2.4 keV X-ray luminosities of $0.4-3.5 \times 10^{40} erg s^{-1}$. The X-ray nebulae are roughly co-spatial with the large-scale radio emission, suggesting that both are produced by large-scale galactic outflows. Assuming pressure balance between the radio and X-ray plasmas, the X-ray filling factor is $\gapprox 10^4$ times larger than the radio plasma filling factor, suggesting that large-scale outflows in Seyfert galaxies are predominantly winds of thermal X-ray emitting gas. We favor an interpretation in which large-scale outflows originate as AGN-driven jets that entrain and heat gas on kpc scales as they make their way out of the galaxy. AGN- and starburst-driven winds are also possible explanations in cases where the winds are oriented along the rotation axis of the galaxy disk.