The Luminosity Function and Density Distribution of Disk Population Stars

The density distribution and luminosity function of the disk population are investigated, using star counts as a function of V and B-V for several thousand stars near the North Galactic Pole. Having estimated the contributions to the counts due to Population II stars and disk giants and subgiants, the remaining stars are assumed to constitute a pure disk-dwarf population. Density distributions for stars in successive (B-V)_0 intervals are calculated and combined to form a composite disk density distribution. The agreement with Oort’s K-giant distribution is satisfactory. There is evidence that dwarfs redder than (B-V)_0=1.4 are concentrated in a narrow layer in the plane, similar to the interstellar gas. Determination of the luminosity function for the reddest disk dwarfs indicates these stars are five to ten times as numerous as was previously thought, thus accounting for a significant fraction of the missing mass in the solar neighborhood. The luminosity function is extrapolated to estimate the contribution to the missing mass of main sequence stars fainter than those considered in the analysis

Equivalent Width of Hα in Late-Type Stars

The use of the equivalent width of Ha as a luminosity criterion for late-type stars is investigated. The method is found to be no more accurate than MK luminosity classifications. Two spectrograms are presented which indicate a change in the Ha equivalent width in 22 Vul over a three-year period

Reduction and analysis of VLA maps for 281 radio-loud quasars using the UNLV Cray Y-MP supercomputer

The identification of distorted radio-loud quasars provides a potentially very powerful tool for basic cosmological studies. If large morphological distortions are correlated with membership of the quasars in rich clusters of galaxies, optical observations can be used to identify rich clusters of galaxies at large redshifts. Hintzen, Ulvestad, and Owen (1983, HUO) undertook a VLA A array snapshot survey at 20 cm of 123 radio-loud quasars, and they found that among triple sources in their sample, 17 percent had radio axes which were bent more than 20 deg and 5 percent were bent more than 40 deg. Their subsequent optical observations showed that excess galaxy densities within 30 arcsec of 6 low-redshift distorted quasars were on average 3 times as great as those around undistorted quasars (Hintzen 1984). At least one of the distorted quasars observed, 3C275.1, apparently lies in the first-ranked galaxy at the center of a rich cluster of galaxies (Hintzen and Romanishin, 1986). Although their sample was small, these results indicated that observations of distorted quasars could be used to identify clusters of galaxies at large redshifts. The purpose of this project is to increase the available sample of distorted quasars to allow optical detection of a significant sample of quasar-associated clusters of galaxies at large redshifts

The Luminosity Function and Density Distribution of Disk Population Stars

The density distribution and luminosity function of the disk population are investigated, using star counts as a function of V and B-V for several thousand stars near the North Galactic Pole. Having estimated the contributions to the counts due to Population II stars and disk giants and subgiants, the remaining stars are assumed to constitute a pure disk-dwarf population. Density distributions for stars in successive (B-V)_0 intervals are calculated and combined to form a composite disk density distribution. The agreement with Oort’s K-giant distribution is satisfactory. There is evidence that dwarfs redder than (B-V)_0=1.4 are concentrated in a narrow layer in the plane, similar to the interstellar gas. Determination of the luminosity function for the reddest disk dwarfs indicates these stars are five to ten times as numerous as was previously thought, thus accounting for a significant fraction of the missing mass in the solar neighborhood. The luminosity function is extrapolated to estimate the contribution to the missing mass of main sequence stars fainter than those considered in the analysis

Uncle Jesse and the seven “early career” ladies of the night

Jesse Leonard Greenstein (1909–2002) was apparently a very hard sell when it came to women in astronomy. Early in his autobiography, he wrote of “Miss Payne, a person of wide culture and astronomical knowledge. The obvious discrimination against her as a woman scientist, worthy of normal academic recognition, exacerbated the stressful life she led. She was unhappy, emotional, in a rivalry with Menzel and Plaskett.” She (a.k.a. Cecilia Helena Payne, later Gaposchkin) is the only woman with an explicit mention in that memoir, and Greenstein's impression of her left him uncertain whether women belonged in astronomy. In addition, some of us remember him as saying there was no use in educating women through to a Ph.D. because they only get married and quit

The Relationship Between Black Hole Mass and Velocity Dispersion in Seyfert 1 Galaxies

Black hole masses in active galactic nuclei (AGN) are difficult to measure using conventional dynamical methods, but can be determined using the technique of reverberation mapping. However, it is important to verify that the results of these different methods are equivalent. This can be done indirectly, using scaling relations between the black hole and the host galaxy spheroid. For this purpose, we have obtained new measurements of the bulge stellar velocity dispersion, sigma, in Seyfert 1 galaxies. These are used in conjunction with the M_bh -- sigma relation to validate nuclear black hole masses, M_bh, in active galaxies determined through reverberation mapping. We find that Seyfert galaxies follow the same M_bh -- sigma relation as non-active galaxies, indicating that reverberation mapping measurements of M_bh are consistent with those obtained using other methods. We also reconsider the relationship between bulge absolute magnitude, M_bulge, and black hole mass. We find that Seyfert galaxies are offset from non-active galaxies, but that the deviation can be entirely understood as a difference in bulge luminosity, not black hole mass; Seyfert hosts are brighter than normal galaxies for a given value of their velocity dispersion, perhaps as a result of younger stellar populations.Comment: 12 pages, 8 figures, accepted for publication in the Astrophysical Journa

Uncle Jesse and the seven “early career” ladies of the night

Jesse Leonard Greenstein (1909–2002) was apparently a very hard sell when it came to women in astronomy. Early in his autobiography, he wrote of “Miss Payne, a person of wide culture and astronomical knowledge. The obvious discrimination against her as a woman scientist, worthy of normal academic recognition, exacerbated the stressful life she led. She was unhappy, emotional, in a rivalry with Menzel and Plaskett.” She (a.k.a. Cecilia Helena Payne, later Gaposchkin) is the only woman with an explicit mention in that memoir, and Greenstein's impression of her left him uncertain whether women belonged in astronomy. In addition, some of us remember him as saying there was no use in educating women through to a Ph.D. because they only get married and quit

HST STIS spectroscopy of the triple nucleus of M31: two nested disks in Keplerian rotation around a Supermassive Black Hole

We present HST spectroscopy of the nucleus of M31 obtained with STIS. Spectra taken around the CaT lines at 8500 see only the red giants in the double bright- ness peaks P1 and P2. In contrast, spectra taken at 3600-5100 A are sensitive to the tiny blue nucleus embedded in P2, the lower surface brightness red nucleus. P2 has a K-type spectrum, but the embedded blue nucleus has an A-type spectrum with strong Balmer absorption lines. Given the small likelihood for stellar collisions, a 200 Myr old starburst appears to be the most plausible origin of the blue nucleus. In stellar population, size, and velocity dispersion, the blue nucleus is so different from P1 and P2 that we call it P3. The line-of-sight velocity distributions of the red stars in P1+P2 strengthen the support for Tremaine s eccentric disk model. The kinematics of P3 is consistent with a circular stellar disk in Keplerian rotation around a super-massive black hole with M_bh = 1.4 x 10^8 M_sun. The P3 and the P1+P2 disks rotate in the same sense and are almost coplanar. The observed velocity dispersion of P3 is due to blurred rotation and has a maximum value of sigma = 1183+-201 km/s. The observed peak rotation velocity of P3 is V = 618+-81 km/s at radius 0.05" = 0.19 pc corresponding to a circular rotation velocity at this radius of ~1700 km/s. Any dark star cluster alternative to a black hole must have a half-mass radius <= 0.03" = 0.11 pc. We show that this excludes clusters of brown dwarfs or dead stars on astrophysical grounds.Comment: Astrophysical Journal, Sep 20, 2005, 21 pages including 20 figure

M33: A Galaxy with No Supermassive Black Hole

Galaxies that contain bulges appear to contain central black holes whose masses correlate with the velocity dispersion of the bulge. We show that no corresponding relationship applies in the pure disk galaxy M33. Three-integral dynamical models fit Hubble Space Telescope WFPC2 photometry and STIS spectroscopy best if the central black hole mass is zero. The upper limit is 1500 M_sun. This is significantly below the mass expected from the velocity dispersion of the nucleus and far below any mass predicted from the disk kinematics. Our results suggest that supermassive black holes are associated only with galaxy bulges and not with their disks.Comment: 8 pages, AJ accepted, November issu