Synthetic Galaxy Research Articles

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. To quantify this accuracy, we 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 for galaxies whose effective (half-light) radii range from 070 to 017. We have done the calculations using two synthetic galaxies of effective radii of 070 and 025 with point-spread functions of 01, 03, and 09, full width at half maximum. We have also compared actual observations of three high-redshift galaxies in the cluster Cl 1324+3011 (z = 0.76) made both with the ground-based Keck 10 m telescopes in seeing of about 09 and with the Hubble Space Telescope (HST) with a point-spread function that is approximately 10 times smaller. The conclusion is that HST data can be used as far into the galaxy image as a Petrosian metric radius of η = 1.3 mag, whereas the ground-based data will have systematic errors of up to 2.9 mag in the mean surface brightness at η values of less than 2.2 mag for all but the largest galaxies at redshifts of z ≈ 0.7. In the final section, we compare the differences in derived average surface brightness for nearly circular galaxy images 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 (ab)1/2, where a and b are the semimajor and semiminor 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.

Infrared Imaging of the Gravitational Lens PG 1115+080 with the Subaru Telescope

We present high spatial resolution images of the gravitational-lens system PG 1115+080 taken with the near-infrared camera (CISCO) on the Subaru telescope. The FWHM of the combined image is 0″.32 in the K′-band, yielding spatial resolution of 0″.14 after a deconvolution procedure. This is a first detection of an extended emission adjacent to the A1/A2 components, indicating the presence of a fairly bright emission region with a characteristic angular radius of ∼ 5 mas (40 pc). The near-infrared image of the Einstein ring was extracted in both the J and K′ bands. The J – K′ color is found to be significantly redder than that of a synthetic model galaxy with an age of 3 Gyr, the age of the universe at the quasar redshift.

An Automated Cluster Finder: The Adaptive Matched Filter

We describe an automated method for detecting clusters of galaxies in imaging and redshift galaxy surveys. The Adaptive Matched Filter (AMF) method utilizes galaxy positions, magnitudes, and---when available---photometric or spectroscopic redshifts to find clusters and determine their redshift and richness. The AMF can be applied to most types of galaxy surveys: from two-dimensional (2D) imaging surveys, to multi-band imaging surveys with photometric redshifts of any accuracy (2.5D), to three-dimensional (3D) redshift surveys. The AMF can also be utilized in the selection of clusters in cosmological N-body simulations. The AMF identifies clusters by finding the peaks in a cluster likelihood map generated by convolving a galaxy survey with a filter based on a model of the cluster and field galaxy distributions. In tests on simulated 2D and 2.5D data with a magnitude limit of r' ~ 23.5, clusters are detected with an accuracy of Delta z ~ 0.02 in redshift and ~10% in richness to z < 0.5. Detecting clusters at higher redshifts is possible with deeper surveys. In this paper we present the theory behind the AMF and describe test results on synthetic galaxy catalogs.

Principal component analysis of synthetic galaxy spectra

We analyse synthetic galaxy spectra from the evolutionary models of Bruzual&Charlot and Fioc&Rocca-Volmerange using the method of Principal Component Analysis (PCA). We explore synthetic spectra with different ages, star formation histories and metalicities, and identify the Principal Components (PCs) of variance in the spectra due to these different model parameters. The PCA provides a more objective and informative alternative to diagnostics by individual spectral lines. We discuss how the PCs can be used to estimate the input model parameters and explore the impact of noise in this inverse problem. We also discuss how changing the sampling of the ages and other model parameters affects the resulting PCs. Our first two synthetic PCs agree with a similar analysis on observed spectra obtained by Kennicutt and the 2dF redshift survey. We conclude that with a good enough signal-to-noise (S/N>> 10) it is possible to derive age, star formation history and metallicity from observed galaxy spectra using PCA.

Galaxies with a UV excess in which supernovae have been observed

A list of galaxies with a UV excess in which at least one supernova (SN) has exploded is compiled. Distributions of the linear distances of SN in synthetic galaxies are obtained, constructed for galaxies with a UV excess and normal galaxies. It is shown that SN activity is the same in galaxies with a UV excess and in normal galaxies.

Internal Kinematics of Field Galaxies at Intermediate Redshifts

This paper describes the results of a survey of the internal kinematics of intermediate-redshift (z = 0.25-0.45) field galaxies. Spatially resolved spectra of the [O II] ??3726, 3729 doublet emission line have been obtained for 22 galaxies at the Canada-France-Hawaii Telescope. High spatial resolution has made it possible to extract Vrot sin i and [O II] disk scale lengths from each galaxy spectrum using synthetic galaxy rotation curve fitting. About 25% of the galaxies in the sample have [O II] kinematics unrelated to rotation. [O II] emission is concentrated in the nucleus in these kinematically anomalous galaxies. A Doppler ellipse, similar to those found in local dwarf irregular galaxies, has been observed in a z = 0.35 galaxy. An intermediate-redshift Tully-Fisher (TF) relation, defined by 12 kinematically normal galaxies, shows that these galaxies have a systematically lower rotation velocity (i.e., mass) for their luminosity than expected from the local TF relation. These galaxies would have to fade by ~1.5-2 mag to lie on the local TF relation. This is consistent with starbursting dwarf galaxy models. Although the sample is small, there is also a hint that massive galaxies are not as displaced from the local TF relation as low-mass ones. However, as shown using a large sample of local galaxies, the scatter in the local TF relation is large, especially for late-type galaxies. Sample selection effects, particularly in [O II] emission strength, could be responsible for part of the observed TF evolutionary shift if star formation rates were responsible for the local TF relation scatter. A comparison with other works indicates that a mass-dependent luminosity evolution scenario can explain almost all of the available internal kinematics and surface brightness data.

An imaging K-band survey – II. The redshift survey and galaxy evolution in the infrared

We present a redshift survey of 124 galaxies, from an imaging $K$-band survey complete to $K\simeq 17.3$. The optical-to-infrared colours are consistent with the range expected from synthetic galaxy spectra, although there are some cases of very red nuclei. Our data show no evidence for evolution of the $K$-band luminosity function at $z<0.5$, and the results are well described by a Schechter function with $M_K^*=-22.75\pm0.13+5\log_{10}h$ and $\phi^*=0.026\pm0.003 h^3 {\rm Mpc^{-3}}$. This is a somewhat higher normalization than has been found by previous workers, and it removes much of the excess in faint $K$ and $B$ counts with respect to a no-evolution model. However, we do find evidence for evolution at $z>0.5$: $M_K^*$ is approximately 0.75 mag. brighter at $z=1$. This luminosity evolution is balanced by a reduced normalization at high redshift. The overall evolution is thus opposite to that expected in simple merger-dominated models.

Automated detection of clusters of galaxies

view Abstract Citations (19) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Automated detection of clusters of galaxies. Dodd, R. J. ; MacGillivray, H. T. Abstract The authors describe a method for the automated detection and parametrization of rich clusters of galaxies in deep wide-angle surveys obtained by purely objective means from machine-produced data. The technique is applied to one field of the ESO/SERC Southern Sky survey and also to a variety of synthetic galaxy fields produced from Monte Carlo simulations. The results indicate that clusters of galaxies are generally highly flattened, the distribution of cluster shapes being more elongated than the shapes of elliptical galaxies. The potential of the method for investigation of the geometric properties of clusters by objective means in a much larger sample over a wide area of sky is discussed. Publication: The Astronomical Journal Pub Date: October 1986 DOI: 10.1086/114206 Bibcode: 1986AJ.....92..706D Keywords: Astronomical Photography; Automatic Control; Cluster Analysis; Galactic Clusters; Computational Astrophysics; Ellipticity; Mass Distribution; Monte Carlo Method; Photographic Plates; Sky Surveys (Astronomy); Astronomy full text sources ADS | Related Materials (1) Erratum: 1987AJ.....93.1287D

Spectroscopic evidence for activity in the nuclei of normal spiral galaxies

view Abstract Citations (324) References (75) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectroscopic evidence for activity in the nuclei of normal spiral galaxies. Keel, W. C. Abstract The emission spectra of 29 spiral galaxies with low-ionization emission have been studied in detail, using synthetic galaxy spectra to correct the observed spectra for the contribution of starlight. The resulting emission-line intensities and ratios have been compared to published models of shock-heated and power-law photoionized plasmas. The observed spectra are best described by models in which a weak flat-spectrum (power-law) radiation field photoionizes the gas; this nonthermal continuum is generally too weak to be seen directly in the optical. Broad H-alpha emission, extending over a total velocity range as great as 4000 km/s, is identified in several 'normal' nuclei with strong low-ionization emission. The inferred nonthermal continuum and observed broad permitted lines indicate the presence of low-luminosity active nuclei in most, if not all, spiral galaxies. Publication: The Astrophysical Journal Pub Date: June 1983 DOI: 10.1086/161057 Bibcode: 1983ApJ...269..466K Keywords: Emission Spectra; Galactic Nuclei; H Alpha Line; Interstellar Gas; Photoionization; Spiral Galaxies; Abundance; Astronomical Models; Continuous Spectra; Data Simulation; Nonthermal Radiation; Shock Heating; Spectral Line Width; Spectrophotometry; Astrophysics full text sources ADS | data products SIMBAD (51) NED (34)