IUE observations of Fe 2 galaxies

Repeated observations of the Seyfert 1 galaxies I Zw 1 and II Zw 136, which have very strong Fe II emission lines in the optical region, were made at low resolution with the IUE Satellite. The ultraviolet spectra are very similar: both are variable and show broad emission features of Fe II (especially the UV multiplets 1, 33, 60, 62, and 63) as well as the emission lines usually strong in Seyferts and quasars. The data strongly support the hypothesis that the optical Fe II emission lines are primarily due to collisional excitation and that resonance fluorescence makes only a minor contribution to the excitation of these lines

Kinematics of Ionised Gas in the Barred Seyfert Galaxy NGC 4151

We have determined the structure and kinematics of ionised gas in the weak oval bar of the archetypal Seyfert 1 galaxy, NGC 4151, using the TAURUS Fabry-Perot interferometer to simultaneously map the distribution and kinematics of Hbeta emission. We also present broad-band ultraviolet imaging of the host galaxy, obtained with XMM-Newton, that shows the detailed distribution of star formation in the bar and in the optically-faint outer spiral arms. We compare the distribution and kinematics of ionised gas with that previously determined in neutral hydrogen by Mundell & Shone; we suggest that the distribution of bright, patchy UV emission close to the HI shocks is consistent with ionisation by star clusters that have formed in compressed pre-shock gas. These clusters then travel ballistically through the gaseous shock to ionise gas downstream along the leading edge of the bar. In addition, we detect, for the first time, ionised gas within the shock itself which is streaming to smaller radii in the same manner as the neutral gas.Comment: 9 pages, 8 figures. Accepted by MNRA

ASCA Observation of an X-Ray-Luminous Active Nucleus in Markarian 231

We have obtained a moderately long (100 kilosecond) ASCA observation of the Seyfert 1 galaxy Markarian 231, the most luminous of the local ultraluminous infrared galaxy (ULIRG) population. In the best-fitting model we do not see the X-ray source directly; the spectrum consists of a scattered power-law component and a reflection component, both of which have been absorbed by a column N_H \approx 3 X 10^(22)/cm^2. About 3/4 of the observed hard X-rays arise from the scattered component, reducing the equivalent width of the iron K alpha line. The implied ratio of 1-10 keV X-ray luminosity to bolometric luminosity, L_x/L_bol \sim 2%, is typical of Sy 1 galaxies and radio-quiet QSOs of comparable bolometric luminosities, and indicates that the bolometric luminosity is dominated by the AGN. Our estimate of the X-ray luminosity also moves Mrk 231 in line with the correlations found for AGN with extremely strong Fe II emission. A second source separated by about 2 arcminutes is also clearly detected, and contributes about 25% of the total flux.Comment: 11 pages, 3 figures; to appear in ApJ Letter

The Nuclear Gas Dynamics and Star Formation of Markarian 231

We report adaptive optics H- and K-band spectroscopy of the inner few arcsec of the luminous merger/ULIRG/QSO Mkn231, at spatial resolutions as small as 0.085". For the first time we have been able to resolve the active star forming region close to the AGN using stellar absorption features, finding that its luminosity profile is well represented by an exponential function with a disk scale length 0.18-0.24" (150-200pc), and implying that the stars exist in a disk rather than a spheroid. The stars in this region are also young (10-100Myr), and it therefore seems likely that they have formed in situ in the gas disk, which itself resulted from the merger. The value of the stellar velocity dispersion is a result of the large mass surface density of the disk. The stars in this region have a combined mass of at least 1.6x10^9M_sun, and account for 25-40% of the bolometric luminosity of the entire galaxy. We have detected the 2.12um 1-0S(1) H_2 and 1.64um [FeII] lines out to radii exceeding 0.5". The kinematics for the two lines are very similar to each other as well as to the stellar kinematics, and broadly consistent with the nearly face-on rotating disk reported in the literature and based on interferometric CO1-0 and CO2-1 measurements of the cold gas. However, they suggest a more complex situation in which the inner 0.2-0.3" (200pc) is warped out of its original disk plane. Such a scenario is supported by other observations.Comment: accepted for publication in ApJ; abstract given here is slightly shortene

HST polarization map of the ultraviolet emission from the outer jet in M87 and a comparison with the 2cm radio emission

We present the first high resolution polarization map of the ultraviolet emission from the outer jet in M87. The data were obtained by the Faint Object Camera (FOC) on the Hubble Space Telescope. The polarization map has a resolution of 0.2 arcsec and was derived using data from three linearly polarized images combined with the best available calibration data. The ultraviolet emission is highly polarized (~40\%) with the magnetic vector aligned roughly with the jet axis, except in the region of the brightest knot (Knot A) where the position angle changes abruptly and the magnetic vector becomes perpendicular to the jet axis. A similar behaviour is seen in the 2cm VLA radio polarization map. By aligning the FOC and VLA data, we present ultraviolet--2cm spectral index, depolarization and rotation measure maps. We identify a region of high depolarization adjacent to Knot A. This is the first direct observational evidence that indicates the presence of a cloud or filament of dense thermal material which is mixed with the synchrotron emitting plasma of the jet. The interaction of the jet with this cloud is likely to be responsible for the sudden increase in the brightness of the jet at Knot A due to an induced shock. We suggest that the dark line seen in the 2cm radio data between Knot A and Knot C could be the shadow or magnetotail of the depolarizing cloud in the jet.Comment: uuencoded compressed postscript. The preprint is also available at http://www.ast.cam.ac.uk/preprint/PrePrint.htm

The Narrow-Line Regions of LINERs as Resolved with the Hubble Space Telescope

LINERs exist in the nuclei of a large fraction of luminous galaxies, but their connection with the AGN phenomenon has remained elusive. We present Hubble Space Telescope narrowband [O III]5007 and H-alpha+[N II] emission-line images of the central regions of 14 galaxies with LINER nuclei. The compact, ~1 arcsec-scale, unresolved emission that dominates the line flux in ground-based observations is mostly resolved by HST. The bulk of this emission comes from regions with sizes of tens to hundreds of parsecs that are resolved into knots, filaments, and diffuse gas whose morphology differs from galaxy to galaxy. Most of the galaxies do not show clear linear structures or ionization cones analogous to those often seen in Seyfert galaxies. An exception is NGC 1052, the prototypical LINER, in which we find a 3 arcsec-long (~ 250 pc) biconical structure that is oriented on the sky along the galaxy's radio jet axis. Seven of the galaxies have been shown in previously published HST images to have a bright compact ultraviolet nuclear source, while the other seven do not have a central UV source. Our images find evidence of dust in the nuclear regions of all 14 galaxies, with clear indications of nuclear obscuration in most of the "UV-dark" cases. The data suggest that the line-emitting gas in most LINERs is photoionized by a central source (which may be stellar, nonstellar, or a combination thereof) but that this source is often hidden from direct view. We find no obvious morphological differences between LINERs with detected weak broad H-alpha wings in their spectra and those with only narrow lines. Likewise, there is no clear morphological distinction between objects whose UV spectra are dominated by hot stars (e.g., NGC 4569) and those that are AGN-like (e.g., NGC 4579).Comment: Accepted for publication in the ApJ. 25 pages, 3 tables, 9 JPEG Figure

The Intrinsic Absorber in QSO 2359-1241: Keck and HST Observations

We present detailed analyses of the absorption spectrum seen in QSO 2359-1241 (NVSS J235953-124148). Keck HIRES data reveal absorption from twenty transitions arising from: He I, Mg I, Mg II, Ca II, and Fe II. HST data show broad absorption lines (BALs) from Al III 1857, C IV 1549, Si IV 1397, and N V 1240. Absorption from excited Fe II states constrains the temperature of the absorber to 2000K < T < 10,000K and puts a lower limit of 10^5 cm^{-3} on the electron number density. Saturation diagnostics show that the real column densities of He I and Fe II can be determined, allowing to derive meaningful constraints on the ionization equilibrium and abundances in the flow. The ionization parameter is constrained by the iron, helium and magnesium data to -3.0 < log(U) < -2.5 and the observed column densities can be reproduced without assuming departure from solar abundances. From comparison of the He I and Fe II absorption features we infer that the outflow seen in QSO 2359-1241 is not shielded by a hydrogen ionization front and therefore that the existence of low-ionization species in the outflow (e.g., Mg II, Al III, Fe II) does not necessitate the existence of such a front. We find that the velocity width of the absorption systematically increases as a function of ionization and to a lesser extent with abundance. Complementary analyses of the radio and polarization properties of the object are discussed in a companion paper (Brotherton et al. 2000).Comment: 30 pages, 9 figures, in press with the Ap

Millimeter Interferometric HCN(1-0) and HCO+(1-0) Observations of Luminous Infrared Galaxies

We present the results on millimeter interferometric observations of four luminous infrared galaxies (LIRGs), Arp 220, Mrk 231, IRAS 08572+3915, and VV 114, and one Wolf-Rayet galaxy, He 2-10, using the Nobeyama Millimeter Array (NMA). Both the HCN(1-0) and HCO+(1-0) molecular lines were observed simultaneously and their brightness-temperature ratios were derived. High-quality infrared L-band (2.8-4.1 micron) spectra were also obtained for the four LIRGs to better constrain their energy sources deeply buried in dust and molecular gas. When combined with other LIRGs we have previously observed with NMA, the final sample comprised nine LIRGs (12 LIRGs' nuclei) with available interferometric HCN(1-0) and HCO+(1-0) data-sufficient to investigate the overall trend in comparison with known AGNs and starburst galaxies. We found that LIRGs with luminous buried AGN signatures at other wavelengths tend to show high HCN(1-0)/HCO+(1-0) brightness-temperature ratios as seen in AGN-dominated galaxies, while the Wolf-Rayet galaxy He 2-10 displays a small ratio. An enhanced HCN abundance in the interstellar gas surrounding a strongly X-ray-emitting AGN, as predicted by some chemical calculations, is a natural explanation of our results.Comment: 43 pages, 11 figures, accepted for publication in Astronomical Journal. Higher resolution version is available at http://optik2.mtk.nao.ac.jp/~imanishi/Paper/HCN2/HCN2.pd

Optical Versus Mid-Infrared Spectroscopic Classification of Ultraluminous Infrared Galaxies

The origin of huge infrared luminosities of ultraluminous infrared galaxies (ULIGs) is still in question. Recently, Genzel et al. made mid-infrared (MIR) spectroscopy of a large number of ULIGs and found that the major energy source in them is massive stars formed in the recent starburst activity; i.e., $\sim$ 70% -- 80% of the sample are predominantly powered by the starburst. However, it is known that previous optical spectroscopic observations showed that the majority of ULIGs are classified as Seyferts or LINERs (low-ionization nuclear emission-line regions). In order to reconcile this difference, we compare types of emission-line activity for a sample of ULIGs which have been observed in both optical and MIR. We confirm the results of previous studies that the majority of ULIGs classified as LINERs based on the optical emission-line diagnostics turn to be starburst-dominated galaxies based on the MIR ones. Since the MIR spectroscopy can probe more heavily-reddened, inner parts of the ULIGs, it is quite unlikely that the inner parts are powered by the starburst while the outer parts are powered by non-stellar ionization sources. The most probable resolution of this dilemma is that the optical emission-line nebulae with the LINER properties are powered predominantly by shock heating driven by the superwind activity; i.e., a blast wave driven by a collective effect of a large number of supernovae in the central region of galaxy mergers.Comment: 15 pages, 2 tables, and 3 eps figures. The Astrophysical Journal (Part 1), in pres

Radio Continuum Evidence for Outflow and Absorption in the Seyfert 1 Galaxy Markarian 231

The VLBA and the VLA have been used to image the continuum radio emission from Mrk 231, a Seyfert 1 galaxy and the brightest infrared galaxy in the local universe. The smallest scales reveal a double source less than 2 pc in extent. The components of this central source have minimum brightness temperatures of 10^9 to 10^{10} K, spectral turnovers between 2 and 10 GHz, and appear to define the galaxy nucleus plus the inner regions of a jet. The components may be free-free absorbed or synchtrotron self-absorbed. On larger scales, the images confirm a previously known north-south triple source extending 40 pc and elongated perpendicular to a 350-pc starburst disk. Both lobes show evidence for free-free absorption near 2 GHz, probably due to ionized gas with a density of 1-2 X 10^3 cm^{-3} in the innermost parts of the starburst disk. The absorbing gas may be ionized by the active nucleus or by local regions of enhanced star formation. The elongation of the 40-pc triple differs by 65 deg from that of the 2-pc source. The different symmetry axes on different scales imply strong curvature in the inner part of the radio jet. The radio continuum from the 350-pc disk has a spectral index near -0.4 above 1.4 GHz and is plausibly energized by a massive burst of star formation. On VLA scales, asymmetric and diffuse emission extends for more than 25 kpc. This emission has a steep spectrum, linear polarization exceeding 50% at some locations, and shares the symmetry axis of the 40-pc triple. The diffuse radio source is probably generated by energy deposition from a slow-moving nuclear jet, which conceivably could help energize the off-nuclear starburst as well.Comment: 34 pages, 7 Postscript figures, LaTeX file in AASTeX format, accepted in ApJ, Vol. 516, May 1, 199