arXiv:0809.0260 [ps, pdf, other] Title: The effect of gas-dynamics on semi-analytic modeling of cluster galaxies Authors: A. Saro, G. De Lucia, K. Dolag, S. Borgani Comments: 13 pages, 12 figures, to appear in MNRAS Subjects: Astrophysics (astro-ph) We study the degree to which non-radiative gas dynamics affects the merger histories of haloes along with subsequent predictions from a semi-analytic model (SAM) of galaxy formation. To this aim, we use a sample of dark matter only and non-radiative SPH simulations of four massive clusters. The presence of gas-dynamical processes (e.g. ram-pressure from the hot ICM) makes haloes more fragile in the runs which include gas. This results in a 25 per cent decrease in the total number of subhaloes at z = 0. The impact on the galaxy population predicted by SAMs is complicated by the presence of "orphan" galaxies, i.e. galaxies whose parent substructures are reduced below the resolution limit of the simulation. In the model employed in our study, these galaxies survive for a residual merging time that is computed using a variation of the Chandrasekhar formula. Due to ram-pressure stripping, haloes in gas simulations tend to be less massive than their counterparts in the dark matter simulations. The resulting merging times for satellite galaxies are then longer in these simulations. On the other hand, the presence of gas influences the orbits of haloes making them on average more circular and therefore reducing the estimated merging times with respect to the dark matter only simulation. This effect is particularly significant for the most massive satellites and is (at least in part) responsible for the fact that brightest cluster galaxies in runs with gas have stellar masses which are about 25 per cent larger than those obtained from dark matter only simulations. Our results show that gas-dynamics has only a marginal impact on the statistical properties of the galaxy population, but that its impact on the orbits and merging times of haloes strongly influences the assembly of the most massive galaxies. [ arXiv:0809.0309 [ps, pdf, other] Title: AGN Host Galaxy Morphologies in COSMOS Authors: J. M. Gabor, C. D. Impey, K. Jahnke, B. D. Simmons, J. R. Trump, A. M. Koekemoer, M. Brusa, N. Cappelluti, E. Schinnerer, V. Smolčić, M. Salvato, J. D. Rhodes, B. Mobasher, P. Capak, R. Massey, A. Leauthaud, N. Scoville Comments: 21 pages, 15 figures, Table 2 abridged. Accepted for publication in ApJ Subjects: Astrophysics (astro-ph) We use HST/ACS images and a photometric catalog of the COSMOS field to analyze morphologies of the host galaxies of approximately 400 AGN candidates at redshifts 0.3 < z < 1.0. We compare the AGN hosts with a sample of non-active galaxies drawn from the COSMOS field to match the magnitude and redshift distribution of the AGN hosts. We perform 2-D surface brightness modeling with GALFIT to yield host galaxy and nuclear point source magnitudes. X-ray selected AGN host galaxy morphologies span a substantial range that peaks between those of early-type, bulge-dominated and late-type, disk-dominated systems. We also measure the asymmetry and concentration of the host galaxies. Unaccounted for, the nuclear point source can significantly bias results of these measured structural parameters, so we subtract the best-fit point source component to obtain images of the underlying host galaxies. Our concentration measurements reinforce the findings of our 2-D morphology fits, placing X-ray AGN hosts between early- and late-type inactive galaxies. AGN host asymmetry distributions are consistent with those of control galaxies. Combined with a lack of excess companion galaxies around AGN, the asymmetry distributions indicate that strong interactions are no more prevalent among AGN than normal galaxies. In light of recent work, these results suggest that the host galaxies of AGN at these X-ray luminosities may be in a transition from disk-dominated to bulge-dominated, but that this transition is not typically triggered by major mergers. [16] arXiv:0809.0568 [ps, pdf, other] Title: The Extragalactic Distance Scale without Cepheids Authors: Jeremy Mould, Shoko Sakai Comments: Accepted by ApJ Letters Subjects: Astrophysics (astro-ph) Distances of galaxies in the Hubble Space Telescope Key Project are based on the Cepheid period-luminosity relation. An alternative basis is the tip of the red giant branch. Using archival HST data, we calibrate the infrared Tully-Fisher relation using 14 galaxies with tip of the red giant branch measurements. Compared with the Key Project, a higher value of the Hubble Constant by 10% +/- 7% is inferred. Within the errors the two distance scales are therefore consistent. We describe the additional data required for a conclusive tip of the red giant branch measurement of H_0. arXiv:0809.0692 [ps, pdf, other] Title: How long should an astronomical paper be to increase its Impact? Authors: Krzysztof Zbigniew Stanek Comments: 11 pages, 5 figures Subjects: Astrophysics (astro-ph); Digital Libraries (cs.DL); Physics and Society (physics.soc-ph) Naively, one would expect longer papers to have larger impact (i.e., to be cited more). I tested this expectation by selecting all (~30,000) refereed papers from A&A, AJ, ApJ and MNRAS published between 2000 and 2004. These particular years were chosen so papers analyzed would not be too "fresh", but at the same time length of each article could be obtained via ADS. I find that indeed longer papers published in these four major astronomy journals are on average cited more, with a median number of citations increasing from 6 for articles 2-3 pages long to about 50 for articles ~50 pages long. I do however observe a significant "Letters effect", i.e. ApJ and A&A articles 4 pages long are cited more than articles 5-10 pages long. Also, the very few longest (>80 pages) papers are actually cited less than somewhat shorter papers. For individual journals, median citations per paper increase from 11 for ~9,300 A&A papers to 14 for ~5,300 MNRAS papers, 16 for ~2,550 AJ papers, and 20 for ~12,850 ApJ papers (including ApJ Letters and Supplement). I conclude with some semi-humorous career advice, directed especially at first-year graduate students. arXiv:0809.0766 [ps, pdf, other] Title: The High-Mass End of the Black Hole Mass Function: Mass Estimates in Brightest Cluster Galaxies Authors: E. Dalla Bonta' (1,2), L. Ferrarese (2), E. M. Corsini (1), J. Miralda-Escude' (3), L. Coccato (4), M. Sarzi (5), A. Pizzella (1), A. Beifiori (1) ((1) Dipartimento di Astronomia, Universita' degli Studi di Padova, Italy, (2) Herzberg Institute of Astrophysics, Victoria, CA, (3) Institut de Ciencies de l'Espai, IEEC-CSIC/ICREA, (4) Max-Planck-Institut fuer extraterrestrische Physik, Garching bei Muenchen, Germany, (5) Centre for Astrophysics Research, University of Hertfordshire, Hatfield, UK) Comments: 63 pages, 34 figures, 4 tables, accepted for publication by the Astrophysical Journal Subjects: Astrophysics (astro-ph) We present Hubble Space Telescope imaging and spectroscopic observations of three Brightest Cluster Galaxies, Abell 1836-BCG, Abell 2052-BCG, and Abell 3565-BCG, obtained with the Wide Field and Planetary Camera 2, the Advanced Camera for Surveys and the Space Telescope Imaging Spectrograph. The data provide detailed information on the structure and mass profile of the stellar component, the dust optical depth, and the spatial distribution and kinematics of the ionized gas within the innermost region of each galaxy. Dynamical models, which account for the observed stellar mass profile and include the contribution of a central supermassive black hole (SBH), are constructed to reproduce the kinematics derived from the Halpha and [N II](lambda 6548,6583) emission lines. Secure SBH detection with M_bh=3.61(+0.41,-0.50)x10^9 M_sun and M_bh=1.34(+0.21,-0.19)x10^9 M_sun, respectively, are obtained for Abell 1836-BCG and Abell 3565-BCG, which show regular rotation curves and strong central velocity gradients. In the case of Abell 2052-BCG, the lack of an orderly rotational motion prevents a secure determination, although an upper limit of M_bh < 4.60x10^9 M_sun can be placed on the mass of the central SBH. These measurements represent an important step forward in the characterization of the high-mass end of the SBH mass function.