The morphology-density relation for dwarf galaxies

The morphology-density relation is examined for dwarf galaxies with absolute magnitudes -18 less than or equal to M sub B sub T less than or equal to -12.5, based on a deep photographic survey of nearby groups and clusters of galaxies. Results are given. Compared to dwarf ellipticals, dwarf irregulars form a more extended population in nearby clusters, and may in fact be entirely absent from the cluster cores. The spatial distribution of dwarf ellipticals in clusters depends on luminosity and the presence or absence of nucleation. Nucleated dE's and non-nucleated dE's fainter than M sub B sub T approx. -13.5 are concentrated toward the centers of clusters like the giant E and S0 galaxies. In contrast, non-nucleated dE's brighter than M sub B sub T approx. -14.5 are distributed like the spirals and irregulars. The intrinsic shapes of the bright non-nucleated dE's are similar to those of the dwarf irregulars, suggesting a possible evolutionary connection between these two classes of galaxies

The Tolman Surface Brightness Test for the Reality of the Expansion. II. The Effect of the Point-Spread Function and Galaxy Ellipticity on the Derived Photometric Parameters

To complete the Tolman surface brightness test on the reality of the expansion of the Universe, we need to measure accurately the surface brightness profiles of the high-redshift galaxy sample. We, therefore, investigate the effects of various sizes of point-spread-functions composed of telescope diffraction, CCD pixel resolutions, and ground-based seeing on the measurements of mean surface brightness. We have done the calculations using two synthetic galaxies of effective radii of 0.70" and 0.25" with point-spread functions of 0.1, 0.3, and 0.9 arcseconds. We have also compared actual observations of three high-redshift galaxies in the cluster Cl 1324 + 3011 (z = 0.76) made both with the Keck telescopes in seeing of about 0.9" and with HST which has a PSF that is approximately ten times smaller. The conclusion is that HST data can be used as far into the galaxy image as a Petrosian metric radius of eta = 1.3 magnitudes, whereas the ground-based data will have systematic errors of up to 2.9 magnitudes in the mean surface brightness at eta values of less than 2.2 magnitudes. In the final section, we compare the differences in derived average surface brightness for nearly circular galaxy images compared with highly flattened images. The comparison is made by using the two reduction procedures of (1) integrating the profile curves using circular apertures, and (2) approximating an ``equivalent circular'' galaxy that is highly elongated by using an ``effective'' radius of sqrt{ab}, where a and b are the semi-major and semi-minor axis, respectively, of the best-fitting ellipse. The conclusion is that the two methods of reduction give nearly identical results and that either method can be used to analyze the low and high-redshift galaxy samples used in the Tolman test.Comment: 15 pages, 9 figures; accepted for publication in Astronomical Journa

The Schizophrenic Spectrum of LSR 1610-0040: a Peculiar M Dwarf/Subdwarf

We present a moderate resolution (R=2000), 0.8-4.1 micron spectrum of LSR 1610-0040, a high proper motion star classified as an early-type L subdwarf by Lepine and collaborators based on its red-optical spectrum. The near-infrared spectrum of LSR 1610-0040 does not fit into the (tentative) M/L subdwarf sequence but rather exhibits a mix of characteristics found in the spectra of both M dwarfs and M subdwarfs. In particular, the near-infrared spectrum exhibits a Na I doublet and CO overtone bandheads in the K band, and Al I and K I lines and an FeH bandhead in the H band, all of which have strengths more typical of field M dwarfs. Furthermore the spectrum of Gl 406 (M6 V) provides a reasonably good match to the 0.6-4.1 micron spectral energy distribution of LSR 1610. Nevertheless the near-infrared spectrum of LSR 1610 also exhibits features common to the spectra of M subdwarfs including a strong Ti I multiplet centered at ~0.97 microns, a weak VO band at ~1.06 microns, and possible collision-induced H_2 absorption in the H and K bands. We discuss a number of possible explanations for the appearance of the red-optical and near-infrared spectrum of LSR 1610-0040. Although we are unable to definitively classify LSR 1610-0040, the preponderance of evidence suggests that it is a mildly metal-poor M dwarf. Finally, we tentatively identify a new band of TiO at ~0.93 microns in the spectra of M dwarfs.Comment: Accepted for publication in the Astronomical Journa

Large Magellanic Cloud Distance from Cepheid Variables using Least Squares Solutions

Distance to the Large Magellanic Cloud (LMC) is determined using the Cepheid variables in the LMC. We combine the individual LMC Cepheid distances obtained from the infrared surface brightness method and a dataset with a large number of LMC Cepheids. Using the standard least squares method, the LMC distance modulus can be found from the ZP offsets of these two samples. We have adopted both a linear P-L relation and a ``broken'' P-L relation in our calculations. The resulting LMC distance moduli are 18.48+-0.03 mag and 18.49+-0.04 mag (random error only), respectively, which are consistent to the adopted 18.50 mag in the literature.Comment: 2 pages and 1 figure, to appear in proceeding of "Galaxies in the Local Volume" Sydney 8-13 July 200

Measuring the Hubble Constant with the Hubble Space Telescope

Ten years ago our team completed the Hubble Space Telescope Key Project on the extragalactic distance scale. Cepheids were detected in some 25 galaxies and used to calibrate four secondary distance indicators that reach out into the expansion field beyond the noise of galaxy peculiar velocities. The result was H_0 = 72 +/- 8 km/sec/Mpc and put an end to galaxy distances uncertain by a factor of two. This work has been awarded the Gruber Prize in Cosmology for 2009.Comment: Gruber Prize Lecture to be published in Transactions of the IA

The Detailed Forms of the LMC Cepheid PL and PLC Relations

Possible deviations from linearity of the LMC Cepheid PL and PLC relations are investigated. Two datasets are studied, respectively from the OGLE and MACHO projects. A nonparametric test, based on linear regression residuals, suggests that neither PL relation is linear. If colour dependence is allowed for then the MACHO PL relation is found to deviate more significantly from the linear, while the OGLE PL relation is consistent with linearity. These finding are confirmed by fitting "Generalised Additive Models" (nonparametric regression functions) to the two datasets. Colour dependence is shown to be nonlinear in both datasets, distinctly so in the case of the MACHO Cepheids. It is also shown that there is interaction between the period and colour functions in the MACHO data.Comment: 20 pages, 20 figures, MNRAS accepte

Temperature Differences in the Cepheid Instability Strip Require Differences in the Period-Luminosity Relation in Slope and Zero Point

A graphical and an algebraic demonstration is made to show why the slope and zero point of the Cepheid period-luminosity (P-L) relation is rigidly coupled with the slope and zero point of the Cepheid instability strip in the HR diagram. The graphical demonstration uses an arbitrary (toy) ridge line in the instability strip, while the algebraic demonstration uses the pulsation equation into which the observed P-L relations for the Galaxy and the LMC are put to predict the temperature zero points and slopes of the instability strips. Agreement between the predicted and measured instability strip slopes argue that the observed P-L differences between the Galaxy and LMC are real. In another proof, the direct evidence for different P-L slopes in different galaxies is shown by comparing the Cepheid data in the Galaxy, the combined data in NGC 3351 and NGC 4321, in M31, LMC, SMC, IC 1613, NGC 3109, and in Sextans A+B. The P-L slopes for the Galaxy, NGC 3351, NGC 4321, and M31 are nearly identical and are the steepest in the sample. The P-L slopes decrease monotonically with metallicity in the order listed, showing that the P-L relation is not the same in different galaxies, complicating their use in calibrating the extragalactic distance scale.Comment: 15 pages, 1 table, 4 figures, submitted to The Ap

Environmental Dependence of the Structure of Brightest Cluster Galaxies

We measure the Petrosian structural properties of 33 brightest cluster galaxies (BCGs) at redshifts z<0.1 in X-ray selected clusters with a wide range of X-ray luminosities. We find that some BCGs show distinct signatures in their Petrosian profiles, likely to be due to cD haloes. We also find that BCGs in high X-ray luminosity clusters have shallower surface brightness profiles than those in low X-ray luminosity clusters. This suggests that the BCGs in high X-ray luminosity clusters have undergone up to twice as many equal-mass mergers in their past as those in low X-ray luminosity clusters. This is qualitatively consistent with the predictions of hierarchical structure formation.Comment: 11 pages, accepted for publication in MNRA

Mapping the galactic gravitational potential with peculiar acceleration

It has been suggested recently that the change in cosmological redshift (the Sandage test of expansion) could be observed in the next generation of large telescopes and ultra-stable spectrographs. In a recent paper we estimated the change of peculiar velocity, i.e. the peculiar acceleration, in nearby galaxies and clusters and shown it to be of the same order of magnitude as the typical cosmological signal. Mapping the acceleration field allows for a reconstruction of the galactic gravitational potential without assuming virialization. In this paper we focus on the peculiar acceleration in our own Galaxy, modeled as a Kuzmin disc and a dark matter spherical halo. We estimate the peculiar acceleration for all known Galactic globular clusters and find some cases with an expected velocity shift in excess of 20 cm/sec for observations fifteen years apart, well above the typical cosmological acceleration. We then compare the predicted signal for a MOND (modified Newtonian dynamics) model in which the spherical dark matter halo is absent. We find that the signal pattern is qualitatively different, showing that the peculiar acceleration field could be employed to test competing theories of gravity. However the difference seems too small to be detectable in the near future.Comment: 11 pages, 10 figures, 3 tables, minor changes, accepted for publication by MNRA

Neutrino mass constraint from CMB and its degeneracy with other cosmological parameters

We show that the cosmic microwave background (CMB) data of WMAP can give subelectronvolt limit on the neutrino mass: m_nu < 0.63 eV (95% CL). We also investigate its degeneracy with other cosmological parameters. In particular, we show the Hubble constant derived from the WMAP data decreases considerably when the neutrino mass is a few times 0.1 eV.Comment: 3 pages, 2 figures, prepared for the TAUP2007 Proceeding