We demonstrate that dwarf galaxies (10 super(7) < M sub(stellar) < 10 super(9) M sub(middot in circle), -12 < M sub(r) > -18) with no active star formation are extremely rare (<0.06%) in the field. ...We examine the relative number of quenched versus star-forming dwarf galaxies, defining quenched galaxies as having no Halpha emission (EW sub(H)alpha < 2 A) and a strong 4000 A break. The fraction of quenched dwarf galaxies decreases rapidly with increasing distance from a massive host, leveling off for distances beyond 1.5 Mpc. We define galaxies beyond 1.5 Mpc of a massive host galaxy to be in the field. We demonstrate that there is a stellar mass threshold of M sub(stellar) < 1.0 x 10 super(9) M sub(middot in circle) below which quenched galaxies do not exist in the field. The majority of quenched dwarf galaxies (often classified as dwarf elliptical galaxies) are within 2 virial radii of a massive galaxy, and only a few percent of quenched dwarf galaxies exist beyond 4 virial radii.
We investigate the gas content and baryonic Tully-Fisher relationship for extremely low luminosity dwarf galaxies in the absolute magnitude range -13.5 > M sub(r) - 5 log h sub(70) > -16. The sample ...is selected from the Sloan Digital Sky Survey and consists of 101 galaxies for which we have obtained follow-up H I observations using the Arecibo Observatory and Green Bank Telescope. This represents the largest homogeneous sample of dwarf galaxies at low luminosities with well-measured H I and optical properties. The sample spans a range of environments, from dense groups to truly isolated galaxies. The average neutral gas fraction is (f sub(gas)) = 0.6, significantly exceeding that of typical gas-rich galaxies at higher luminosities. Dwarf galaxies are therefore less efficient at turning gas into stars over their lifetimes. The strong environmental dependence of the gas fraction distribution demonstrates that while internal processes can reduce the gas fractions to roughly f sub(gas) = 0.4, external processes are required to fully remove gas from a dwarf galaxy. The average rotational velocity of our sample is (v sub(rot)) = (W20 sub(i,t)/2) = 50 km s super(-1), based on H I line widths. In this luminosity range, the optical Tully-Fisher relationship has significantly more scatter compared to the baryonic relationship. By including more massive galaxies from the literature, we fit a baryonic Tully-Fisher slope of M sub(bary) 8 v super(3) sub(r) super(.) sub(o) super(7) sub(t) super(0c0.15). This slope compares well with CDM models that assume an equal baryon-to-dark matter ratio at all masses. While gas stripping or other processes may modify the baryon-to-dark matter ratio for dwarfs in the densest environments, the majority of dwarf galaxies in our sample have not preferentially lost significant baryonic mass relative to more massive galaxies.
We use a complete sample of about 140 000 galaxies from the Sloan Digital Sky Survey (SDSS) to study the size distribution of galaxies and its dependence on their luminosity, stellar mass and ...morphological type. The large SDSS data base provides statistics of unprecedented accuracy. For each type of galaxy, the size distribution at given luminosity (or stellar mass) is well described by a log-normal function, characterized by its median and dispersion σln R. For late-type galaxies, there is a characteristic luminosity at Mr,0∼−20.5 (assuming h= 0.7) corresponding to a stellar mass M0∼ 1010.6 M⊙. Galaxies more massive than M0 have and σln R∼ 0.3, while less massive galaxies have and σln R∼ 0.5. For early-type galaxies, the relation is significantly steeper, , but the σln R–M relation is similar to that of bright late-type galaxies. Faint red galaxies have sizes quite independent of their luminosities. We use simple theoretical models to interpret these results. The observed relation for late-type galaxies can be explained if the fraction of baryons that form stars is as predicted by the standard feedback model. Fitting the observed σln R–M relation requires in addition that the bulge/disc mass ratio be larger in haloes of lower angular momentum and that the bulge material transfers part of its angular momentum to the disc. This can be achieved if bulge formation occurs so as to maintain a marginally stable disc. For early-type galaxies, the observed σln R–M relation is inconsistent with formation through single major mergers of present-day discs. It is consistent with formation through repeated mergers, if the progenitors have properties similar to those of faint ellipticals or Lyman break galaxies and merge from relatively strongly bound orbits.
Weak lensing is emerging as a powerful observational tool to constrain cosmological models, but is at present limited by an incomplete understanding of many sources of systematic error. Many of these ...errors are multiplicative and depend on the population of background galaxies. We show how the commonly cited geometric test, which is rather insensitive to cosmology, can be used as a ratio test of systematics in the lensing signal at the 1 per cent level. We apply this test to the galaxy-galaxy lensing analysis of the Sloan Digital Sky Survey (SDSS), which at present is the sample with the highest weak lensing signal-to-noise ratio and has the additional advantage of spectroscopic redshifts for lenses. This allows one to perform meaningful geometric tests of systematics for different subsamples of galaxies at different mean redshifts, such as brighter galaxies, fainter galaxies and high-redshift luminous red galaxies, both with and without photometric redshift estimates. We use overlapping objects between SDSS and the DEEP2 and 2df-Sloan LRG and Quasar (2SLAQ) spectroscopic surveys to establish accurate calibration of photometric redshifts and to determine the redshift distributions for SDSS. We use these redshift results to compute the projected surface density contrast Δσ around 259 609 spectroscopic galaxies in the SDSS; by measuring Δσ with different source samples we establish consistency of the results at the 10 per cent level (1σ). We also use the ratio test to constrain shear calibration biases and other systematics in the SDSS survey data to determine the overall galaxy-galaxy weak lensing signal calibration uncertainty. We find no evidence of any inconsistency among many subsamples of the data.
We examine the relationship between environment and the luminosities, surface brightnesses, colors, and profile shapes of luminous galaxies in the Sloan Digital Sky Survey (SDSS). For the SDSS ...sample, galaxy color is the galaxy property most predictive of the local environment. Galaxy color and luminosity--measures of the star formation history--jointly comprise the most predictive pair of properties. At fixed luminosity and color, density is not closely related to surface brightness or to Sersic index--measures of galaxy structure. In the text, we discuss what measurable residual relationships exist, generally finding that at red colors and fixed luminosity, the mean density decreases at the highest surface brightnesses and Sersic indices. In general, these results suggest that the structural properties of galaxies are less closely related to galaxy environment than are their masses and star formation histories.
We examine a sample of low-redshift (10 h super(-1) Mpc < d< 150 h super(-1) Mpc) field galaxies including galaxies with luminosities as low as M sub(r) - 5 log h 6 -12.5, selected from the Sloan ...Digital Sky Survey Data Release 2 (SDSS DR2). The sample is unique in containing galaxies of extremely low luminosities in a wide range of environments, selected with uniform and well-understood criteria. We present the luminosity function, as well as the broadband properties, of low-luminosity galaxies in this sample. A Schechter function is an insufficient parameterization of the r-band luminosity function; there is an upturn in the slope for M sub(r) - 5 log h > -18. The resulting slope at low luminosities in this sample is a sub(2) 6 -1.3. However, we almost certainly miss a large number of galaxies at very low luminosities due to low surface brightness selection effects, and we estimate that the true low-luminosity slope may be as steep as or steeper than a sub(2) 6 -1.5. The results here are consistent with previous SDSS results and, in the g band, roughly consistent with the results of the Two Degree Field Galaxy Redshift Survey. Extremely low luminosity galaxies are predominantly low surface brightness, exponential disks, the majority of which are red.
We study the luminosity and color dependence of the galaxy two-point correlation function in the Sloan Digital Sky Survey, starting from a sample of 6200,000 galaxies over 2500 deg super(2). We ...concentrate our analysis on volume-limited subsamples of specified luminosity ranges, for which we measure the projected correlation function w sub(p)(r sub(p)), which is directly related to the real-space correlation function y(r). The amplitude of w sub(p)(r sub(p)) rises continuously with luminosity from M sub(r) - -17.5 to M sub(r) - -22.5, with the most rapid increase occurring above the characteristic luminosity L sub(*) (M sub(r) - -20.5). Over the scales 0.1 h super(-1) Mpc < r sub(p) < 10 h super(-1) Mpc, the measurements for samples with M sub(r) > -22 can be approximated, imperfectly, by power-law three-dimensional correlation functions y(r) = (r/r sub(0)) super(-g) with g - 1.8 and r sub(0)(L sub(*)) - 5.0 h super(-1) Mpc. The brightest subsample, -23 < M sub(r) < -22, has a significantly steeper y(r). When we divide samples by color, redder galaxies exhibit a higher amplitude and steeper correlation function at all luminosities. The correlation amplitude of blue galaxies increases continuously with luminosity, but the luminosity dependence for red galaxies is less regular, with bright red galaxies exhibiting the strongest clustering at large scales and faint red galaxies exhibiting the strongest clustering at small scales. We interpret these results using halo occupation distribution (HOD) models assuming concordance cosmological parameters. For most samples, an HOD model with two adjustable parameters fits the w sub(p)(r sub(p)) data better than a power law, explaining inflections at r sub(p) 6 1-3 h super(-1) Mpc as the transition between the one-halo and two-halo regimes of y(r). The implied minimum mass for a halo hosting a central galaxy more luminous than L grows steadily, with M sub(min) 8 L at low luminosities and a steeper dependence above L sub(*). The mass at which a halo has, on average, one satellite galaxy brighter than L is M sub(1) - 23M sub(min) (L), at all luminosities. These results imply a conditional luminosity function (at fixed halo mass) in which central galaxies lie far above a Schechter function extrapolation of the satellite population. The HOD model fits nicely explain the color dependence of w sub(p)(r sub(p)) and the cross correlation between red and blue galaxies. For galaxies with M sub(r) < -21, halos slightly above M sub(min) have blue central galaxies, while more massive halos have red central galaxies and predominantly red satellite populations. The fraction of blue central galaxies increases steadily with decreasing luminosity and host halo mass. The strong clustering of faint red galaxies follows from the fact that nearly all of them are satellite systems in high-mass halos. The HOD fitting results are in good qualitative agreement with the predictions of numerical and semianalytic models of galaxy formation.
A New Milky Way Dwarf Galaxy in Ursa Major Willman, Beth; Dalcanton, Julianne J; Martinez-Delgado, David ...
Astrophysical journal/The Astrophysical journal,
06/2005, Letnik:
626, Številka:
2
Journal Article
Recenzirano
Odprti dostop
In this Letter, we report the discovery of a new dwarf satellite to the Milky Way, located at ( alpha sub(2000), delta sub(2000)) = (158 degree .72, 51 degree .92) in the constellation of Ursa Major. ...This object was detected as an overdensity of red, resolved stars in Sloan Digital Sky Survey data. The color-magnitude diagram of the Ursa Major dwarf looks remarkably similar to that of Sextans, the lowest surface brightness Milky Way companion known, but with approximately an order of magnitude fewer stars. Deeper follow-up imaging confirms that this object has an old and metal-poor stellar population and is similar to 100 kpc away. We roughly estimate M sub(V) = -6.75 and r sub(1/2) = 250 pc for this dwarf. Its luminosity is several times fainter than the faintest known Milky Way dwarf. However, its physical size is typical for dwarf spheroidal galaxies. Even though its absolute magnitude and size are presently quite uncertain, Ursa Major is likely the lowest luminosity and lowest surface brightness galaxy yet known.
We report the intermediate-scale (0.3-40 h super(-1) Mpc) clustering of 35,000 luminous early-type galaxies at redshifts 0.16-0.44 from the Sloan Digital Sky Survey. We present the redshift space ...two-point correlation function y(s), the projected correlation function w sub(p)(r sub(p)), and the deprojected real space correlation function y(r), for approximately volume-limited samples. As expected, the galaxies are highly clustered, with the correlation length varying from 9.8 c 0.2 to 11.2 c 0.2 h super(-1) Mpc, dependent on the specific luminosity range. For the -23.2 < M sub(g) < -21.2 sample, the inferred bias relative to that of L* galaxies is 1.84 c 0.11 for 1 h super(-1) Mpc < r sub(p) 10 h super(-1) Mpc, with yet stronger clustering on smaller scales. We detect luminosity-dependent bias within the sample but see no evidence for redshift evolution between z = 0.2 and z = 0.4. We find a clear indication for deviations from a power-law in the real space correlation function, with a dip at 62 h super(-1) Mpc scales and an upturn on smaller scales. The precision measurements of these clustering trends offer new avenues for the study of the formation and evolution of these massive galaxies.
We test the homogeneity of the universe at z similar to 0.3 with the luminous red galaxy (LRG) spectroscopic sample of the Sloan Digital Sky Survey. First, the mean number N(R) of LRGs within ...completely surveyed LRG-centered spheres of comoving radius R is shown to be proportional to R super(3) at radii greater than R similar to 70 h super(-1) Mpc. The test has the virtue that it does not rely on the assumption that the LRG sample has a finite mean density; its results show, however, that there is such a mean density. Second, the survey sky area is divided into 10 disjoint solid angular regions, and the fractional rms density variations of the LRG sample in the redshift range 0.2 < z < 0.35 among these ( similar to 2 x 10 super(7) h super(-3) Mpc super(3)) regions is found to be 7% of the mean density. This variance is consistent with typical biased Lambda CDM models and puts very strong constraints on the quality of SDSS photometric calibration.
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