Seyfert-Type Dependences of Narrow Emission-Line Ratios and Physical Properties of High-Ionization Nuclear Emission-Line Regions in Seyfert Galaxies

In order to examine how narrow emission-line flux ratios depend on the Seyfert type, we compiled various narrow emission-line flux ratios of 355 Seyfert galaxies from the literature. We present in this paper that the intensity of the high-ionization emission lines, [Fe VII]6087, [Fe X]6374 and [Ne V]3426, tend to be stronger in Seyfert 1 galaxies than in Seyfert 2 galaxies. In addition to these lines, [O III]4363 and [Ne III]3869, whose ionization potentials are not high (< 100 eV), but whose critical densities are significantly high (> 10^7 cm^-3), also exhibit the same tendency. On the other hand, the emission-line flux ratios among low-ionization emission lines do not show such a tendency. We point out that the most plausible interpretation of these results is that the high-ionization emission lines arise mainly from highly-ionized, dense gas clouds, which are located very close to nuclei, and thus can be hidden by dusty tori. To examine the physical properties of these highly-ionized dense gas clouds, photoionization model calculations were performed. As a result, we find that the hydrogen density and the ionization parameter of these highly-ionized dense gas clouds are constrained to be n_H > 10^6 cm^-3 and U > 10^-2, respectively. These lower limits are almost independent both from the metallicity of gas clouds and from the spectral energy distribution of the nuclear ionizing radiation.Comment: 32 pages, to appear in Publications of the Astronomical Society of Japa

How Do We See the Nuclear Region (r < 0.1 pc) of Narrow-Line Seyfert 1 Galaxies?

We propose two statistical tests to investigate how we see the nuclear region (r < 0.1 pc) of Narrow-Line Seyfert 1 galaxies (NLS1s). 1) The high-ionization nuclear emission-line region (HINER) test: Seyfert 1 galaxies (S1s) have systematically higher flux ratios of [Fe VII] lambda 6087 to [O III] lambda 5007 than Seyfert 2 galaxies (S2s). This is interpreted in that a significant part of the [Fe VII] lambda 6087 emission arises from the inner walls of dusty tori that cannot be seen in S2s (Murayama & Taniguchi 1998a,b). 2) The mid-infrared test: S1s have systematically higher flux ratios of the L band (3.5 micrometer) to the IRAS 25 micrometer band than S2s. This is also interpreted in that a significant part of the L band emission arises from the inner walls of dusty tori, because the tori are optically thick enough to absorb the L band emission if the tori are viewed nearly edge on (Murayama et al. 2000). Applying these tests to a sample of NLS1s, we have found that the NLS1s possibly have nearly the same properties as S1s.Comment: Contributed talk presented at the Joint MPE,AIP,ESO workshop on NLS1s, Bad Honnef, Dec. 1999, to appear in New Astronomy Reviews; also available at http://wave.xray.mpe.mpg.de/conferences/nls1-worksho

Clustering Properties of Low-Luminosity Star-Forming galaxies at z = 0.24 and 0.40 in the Subaru Deep Field

We present our analysis on the clustering properties of star-forming galaxies selected by narrow-band excesses in the Subaru Deep Field. Specifically we focus on Halpha emitting galaxies at z = 0.24 and z = 0.40 in the same field, to investigate possible evolutionary signatures of clustering properties of star-forming galaxies. Based on the analysis on 228 Halpha emitting galaxies with 39.8 < log L(Halpha) < 40.8 at z = 0.40, we find that their two-point correlation function is estimated as xi = (r/1.62^{+0.64}_{-0.50} Mpc)^{-1.84 +/- 0.08}. This is similar to that of Halpha emitting galaxies in the same Halpha luminosity range at z = 0.24, xi = (r/1.88^{+0.60}_{-0.49} Mpc)^{-1.89 +/- 0.07}. These correlation lengths are smaller than those for the brighter galaxy sample studied by Meneux et al. (2006) in the same redshift range. The evolution of correlation length between z = 0.24 and z = 0.40 is interpreted by the gravitational growth of the dark matter halos.Comment: 16 pages, 7 figures, PASJ, Vol.60, No.6, in pres

An Intermediate-band imaging survey for high-redshift Lyman Alpha Emitters: The Mahoroba-11

We present results of our intermediate-band optical imaging survey for high-$z$ Ly$\alpha$ emitters (LAEs) using the prime focus camera, Suprime-Cam, on the 8.2m Subaru Telescope. In our survey, we use eleven filters; four broad-band filters ($B$, $R_{\rm c}$, $i^\prime$, and $z^\prime$) and seven intermediate-band filters covering from 500 nm to 720 nm; we call this imaging program as the Mahoroba-11. The seven intermediate-band filters are selected from the IA filter series that is the Suprime-Cam intermediate-band filter system whose spectral resolution is $R = 23$. Our survey has been made in a $34^\prime \times 27^\prime$ sky area in the Subaru XMM Newton Deep Survey field. We have found 409 IA-excess objects that provide us a large photometric sample of strong emission-line objects. Applying the photometric redshift method to this sample, we obtained a new sample of 198 LAE candidates at $3 < z < 5$. We found that there is no evidence for evolution of the number density and the star formation rate density for LAEs with $\log L({\rm Ly}\alpha) ({\rm erg s^{-1}}) > 42.67$ between $z \sim 3$ and 5.Comment: 46 pages, 15 figures, PASJ, Vol.57, No.6, in pres

New Supporting Evidence for the Overdensity of Galaxies around the Radio-Loud Quasar SDSS J0836+0054 at z =5.8

Recently, Zheng et al. (2005) found evidence for an overdensity of galaxies around a radio-loud quasar, SDSS J0836+0054, at z=5.8 (a five arcmin$^2$ region). We have examined our deep optical imaging data (B, V, r', i', z', and NB816) taken with the Suprime-Cam on the Subaru Telescope. The NB816 narrow-band filter (lambda_c = 815 nm and $\Delta\lambda = 12$ nm) is suitable for searching for Ly$\alpha$ emitters at $z\approx 5.7$. We have found a new strong Ly$\alpha$ emitter at $z \approx 5.7$ close to object B identified by Zheng et al. Further, the non detection of the nine objects selected by Zheng et al. (2005) in our B, V, and r' images provides supporting evidence that they are high-z objects.Comment: 5 pages, 1 figure, accepted for PAS