Average Rotation Curves of Disk Galaxies

1. MIN [–22.8, –22.4) 6 [–22.4, –22.0) 36 [–22.0, –21.6) 120 [–21.6, –21.2) 227 [–21.2, –20.8) 291 [–20.8, –20.4) 332 [–20.4, –20.0) 299 [–20.0, –19.6) 254 [–19.6, –19.2) 191 [–19.2, –18.4) 177 [–18.4, –16.4) 79 SDSS DR1 RA: 9.045o, DEC: 14.380o Scale: 0.15’’/px 10’’ N W Calibration of the SDSS Spectroscopic Line Width Scaling RelationsBarbara Catinella (NAIC & Cornell U.), Martha P. Haynes, & Riccardo Giovanelli (Cornell U.) Abstract SDSS Line Width Calibration: Simulations The determination of the rotational parameters of disk galaxies is of crucial importance for several areas of observational cosmology, including studies of galaxy formation and evolution over cosmic time. N-body cosmological simulations suggest that disk scaling relations such as the Tully-Fisher (TF) relation should change as galaxies evolve, but recent studies, based on optical spectroscopy of modest numbers of spiral galaxies, have reached conflicting conclusions. The Sloan Digital Sky Survey (SDSS) promises to provide a huge, homogeneous data base of line widths for galaxies with an average redshift z~0.11, over 100,000 of which might be useful for TF applications. Since the SDSS line widths are based on fiber spectroscopy, however, they must be corrected for their aperture bias before they can be directly applied to scaling relations. We analyzed a sample of ~3000 low redshift galaxies with I-band photometry and long-slit H+[NII] spectroscopy to derive the average properties of their rotation curves (RCs) as a function of luminosity, and used the results to simulate, and statistically correct for, the SDSS aperture bias. We are also conducting observations at the Arecibo and Kitt Peak Observatories to calibrate the SDSS line widths, and to test the results of our simulations. This work is supported by a NAIC pre-doctoral research grant at the Arecibo Observatory, and by NSF grants AST-9900695 and AST-0307396. We present here preliminary results of our simulation to statistically correct the SDSS line width measurements for their aperture bias, thus recovering rotational widths that can be used in scaling relations such as the TF. Galaxies are modelled as infinitely thin, pure exponential disks, with exponential H SB profiles; a simple relation between H and I-band scale lengths is assumed (r = rI /0.64), based on a relation determined by Ryder and Dopita (1994); future work will make use of results by R. A. Koopmann. Velocity fields are described by Polyex models, with parameters dependent on MI as determined by our results on average RCs; RC extents are assigned on the basis of the frequency distribution of our own data. Other simulated quantities include inclinations, redshifts, and seeing. Mock catalogs of galaxies are generated and “observed” through a 3´´ aperture, and using a simulated SDSS spectrograph. Total and aperture H profiles are measured by fitting Gaussian functions. i  30 30 < i < 60 Average Rotation Curves of Disk Galaxies i  60 Polyex model fits to the data: Ratio between line width measured through a 3´´ aperture and full width of the total H profile as a function of redshift for a mock catalog of galaxies with flat RC (seeing FWHM= 1.7´´). Simulated profiles for a galaxy with flat RC and different values of inclination and redshift (seeing FWHM= 1.7´´). Solid line and points: total and aperture H profiles; dotted line: Gaussian fit to the points. Left: z=0.2; right: z=0.4; top: i= 20; bottom: i= 80. Arecibo HI Detection of a SDSS galaxy at z=0.19 (1193 MHz) Tint = 370 min (148 min on-source) • We derived average rotation curves in 11 luminosity classes according to the following procedure: • Each RCs is folded around its center of symmetry; the spatial coordinate r is normalized to the optical radius Ropt of the galaxy (i.e., the radius encompassing 83% of the total integrated light), and the velocities are deprojected to edge-on view • All the RCs are resampled at fixed r/Ropt positions (with a 4-point linear interpolation), to assure that the resulting average RCs are not biased toward nearer galaxies, which are characterized by a denser spatial sampling • The resampled RCs are binned into luminosity classes (the MI intervals are shown next to the left panel, along with the number N of objects in each bin). Each RC is normalized to the average velocity of the corresponding MI class, computed over the spatial range  = 0.5-0.8 r/Ropt • Mean velocities and variances are calculated for each grid value of r/Ropt for which there are N4 valid samples, and for each luminosity class In order to explore the cross-calibration of the HI, H+[NII] and SDSS line width relations, we conducted observations using both the Arecibo and the Kitt Peak Mayall telescopes in 2003. The targets were selected from the SDSS spectroscopic survey, based on their inclination, H line width, undisturbed spiral morphology, and isolation. We show here the SDSS image and a preliminary result for AGC 101750, the highest redshift HI detection in our sample so far. The smoothed HI line profile has been obtained by combining total power ON-OFF pairs acquired during 4 nights spread over a period of several weeks in Fall 2003. The observed HI line width (W50) is 546 km/s, the SDSS H FWMH is 381 km/s. The use of a 1120-1220 MHz filter on the L-band wide receiver proved critical for minimizing the impact of radio interference. Additional observing time has been granted for this project at the Arecibo Observatory in the Spring 2004. The left panel shows our results (data points). We excluded from our analysis galaxies with inclination i  80, since internal extinction significantly affects the inner slope of their RCs. We also show Polyex model fits to the data (red), and the dependence of the model coefficients on I-band absolute magnitude (right panel; H0=70 km s-1 Mpc-1).