Astrophysics and Astronomy Commons^™

Spiral Disk Opacity From Occulting Galaxy Pairs In The Sloan Digital Sky Survey., Benne W. Holwerda, W. C. Keel, A. Bolton

Faculty and Staff Scholarship

A spiral galaxy partially overlapping a more distant elliptical offers a unique opportunity to measure the dust extinction in the foreground spiral. From the Sloan Digital Sky Survey (SDSS) DR4 spectroscopic sample, we selected 83 occulting galaxy pairs and measured disk opacity over the redshift range z ¼ 0:0Y0:2 with the goal of determining the recent evolution of disk dust opacity. The enrichment of the ISM changes over the lifetime of a disk, and it is reasonable to expect the dust extinction properties of spiral disks as a whole to change over their lifetime. When they do, the change will …

The Opacity Of Spiral Galaxy Disks. Viii. Structure Of The Cold Ism., Benne W. Holwerda, B. Draine, K. D. Gordon, R. A. Gonzalez, D. Calzetti, M. Thornley, B. Buckalew, Ronald J. Allen, P C. Van Der Kruit

Faculty and Staff Scholarship

The quantity of dust in a spiral disk can be estimated using the dust’s typical emission or the extinction of a known source. In this paper we compare two techniques, one based on emission and one on absorption, applied to sections of 14 disk galaxies. The two measurements reflect, respectively, the average and apparent optical depth of a disk section. Hence, they depend differently on the average number and optical depth of ISM structures in the disk. The small-scale geometry of the cold ISM is critical for accurate models of the overall energy budget of spiral disks. ISM geometry, relative …

Gaps In The Cloud Cover? : Comparing Extinction Measures In Spiral Disks., Benne W. Holwerda, M. Meyer, M. W. Regan, D. Calzetti, K. D. Gordon, J. D. Smith, D. Dale, C. W. Engelbracht, T. Jarrett, M. Thornley, C. Bot, B. Buckalew, R. C. Kennicutt, R. A. Gonzalez

Faculty and Staff Scholarship

Dust in galaxies can be mapped either by the FIR/submillimeter emission, the optical or infrared reddening of starlight, or the extinction of a known background source. We compare two dust extinction measurements for a set of 15 sections in 13 nearby galaxies to determine the scale of the dusty interstellar medium ( ISM ) responsible for disk opacity: one using stellar reddening and the other a known background source. In our earlier papers, we presented extinction measurements of 29 galaxies, based on calibrated counts of distant background objects identified though foreground disks in Hubble Space Telescope WFPC2 images. For the …

Stellar Populations Across The Ngc 4244 Truncated Galactic Disk., Roelof De Jong, A. C. Seth, D. Radburn-Smith, E. F. Bell, T. M. Brown, J. S. Bullock, S. Courteau, J. J. Dalcanton, H. C. Ferguson, P. Goudfrooij, S. Holfeltz, Benne W. Holwerda, C. Purcell, J. Sick, D. B. Zucker

Faculty and Staff Scholarship

We use the Hubble Space Telescope ACS to study the resolved stellar populations of the nearby, nearly edgeon galaxy NGC 4244 across its outer disk surface density break. The stellar photometry allows us to study the distribution of different stellar populations and reach very low equivalent surface brightnesses. We find that the break occurs at the same radius for young, intermediate-age, and old stars. The stellar density beyond the break drops sharply by a factor of at least 600 in 5 kpc. The break occurs at the same radius independent of height above the disk, but is sharpest in the …

A Dust Component ~2 Kpc Above The Plane In Ngc 891., P. Kamphuis, Benne W. Holwerda, R. J. Allen, R. F. Peletier, P. C. Van Der Kruit

Faculty and Staff Scholarship

Context.The halo of NGC 891 has been the subject of studies for more than a decade. One of its most striking features is the large asymmetry in H emission. In this letter, we will take a quantitative look at this asymmetry at different wavelengths for the first time.
Aims.We suggest that NGC 891 is intrinsically almost symmetric and the large asymmetry in H emission is mostly due to dust attenuation. We will quantify the additional optical depth needed to cause the observed asymmetry in this model.
Methods.By comparing large strips on the North East side of the …

Wide-Field Survey Of Globular Clusters In M31. I. A Catalog Of New Clusters, Sang Chul Kim, Myung Gyoon Lee, Doug Geisler, Ata Sarajedini, Hong Soo Park, Ho Seong Hwang, William E. Harris, Juan C. Seguel, Ted Von Hippel

Publications

We present the result of a wide-field survey of globular clusters (GCs) in M31 covering a 3^o x 3^o field centered on M31.We have searched for GCs on CCD images taken with Washington CMT₁ filters at the KPNO 0.9 m telescope using the following steps: (1) inspection of morphological parameters given by the SExtractor package such as stellarity, full width at half-maximum, and ellipticity; (2) consulting the spectral types and radial velocities obtained from spectra taken with the Hydra spectrograph at the WIYN 3.5 m telescope; and (3) visual inspection of the images of each object. We …

The Rotation Velocity Attributable To Dark Matter At Intermediate Radii In Disk Galaxies, Stacy S. Mcgaugh

Faculty Scholarship

We examine the amplitude of the rotation velocity that can be attributed to the dark matter halos of disk galaxies, focusing on well-measured intermediate radii. The data for 60 galaxies spanning a large range of mass and Hubble types, taken together, are consistent with a dark halo velocity log Vh = C + B log R with C = 1.47-0.19+0.15 and B ≈1/2 over the range of 1 < R < 74 kpc. The range in C stems from different choices of the stellar mass estimator, from minimum to maximum disk. For all plausible choices of stellar mass, the implied densities of the dark halos are lower than expected from structure formation simulations in ACDM, which anticipate C > 1.6. This problem is not specific to a particular type of galaxy or to the innermost region of the halo (cusp or core); the velocity attributable to dark matter is too low …

Erratum: A Catalog Of Edge-On Disk Galaxies: From Galaxies With A Bulge To Superthin Galaxies, Stefan Kautsch, E. K. Grebel, F. D. Barazza, J. S. Gallagher

Chemistry and Physics Faculty Articles

Erratum

Evolution Of Stellar Bars In Live Axisymmetric Halos: Recurrent Buckling And Secular Growth, Inma Martinez-Valpuesta, Isaac Shlosman, Clayton Heller

Physics & Astronomy: Faculty Publications

Evolution of stellar bars in disk galaxies is accompanied by dynamical instabilities and secular changes. Following the vertical buckling instability, the bars are known to weaken dramatically and develop a pronounced boxy/ peanut shape when observed edge-on. Using high-resolution N-body simulations of stellar disks embedded in live axisymmetric dark matter halos, we have investigated the long-term changes in the bar morphology, specifically the evolution of the bar size, its vertical structure, and the exchange of angular momentum. We find that following the initial buckling, the bar resumes its growth from deep inside the corotation radius and follows the ultraharmonic resonance …

A Catalog Of Edge-On Disk Galaxies: From Galaxies With A Bulge To Superthin Galaxies, Stefan Kautsch, E. K. Grebel, F. D. Barazza, J. S. Gallagher

Chemistry and Physics Faculty Articles

Spiral galaxies range from bulge-dominated early-type galaxies to late types with little or no bulge. Cosmological models do not predict the formation of disk-dominated, essentially bulgeless galaxies, yet these objects exist. A particularly striking and poorly understood example of bulgeless galaxies are flat or superthin galaxies with large axis ratios. We therefore embarked on a study aimed at a better understanding of these enigmatic objects, starting by compiling a statistically meaningful sample with well-defined properties. The disk axis ratios can be most easily measured when galaxies are seen edge-on. We used data from the Sloan Digital Sky Survey (SDSS) in …

The Opacity Of Spiral Galaxy Disks. V. Dust Opacity, Hi Distributions And Sub-Mm Emission., Benne W. Holwerda, R. A. Gonzalez, Ronald J. Allen, P. C. Van Der Kruit

Faculty and Staff Scholarship

The opacity of spiral galaxy disks, from counts of distant galaxies, is compared to HI column densities. The opacity measurements are calibrated using the “Synthetic Field Method” from González et al. (1998, ApJ, 506, 152), Holwerda et al. (2005a, AJ, 129, 1381). When compared for individual disks, the HI column density and dust opacity do not seem to be correlated as HI and opacity follow different radial profiles. To improve statistics, an average radial opacity profile is compared to an average HI profile. Compared to dust-to-HI estimates from the literature, more extinction is found in this profile. This difference may …

The Opacity Of Spiral Galaxy Disks Vii. The Accuracy Of Galaxy Counts As An Extinction Probe., Benne W. Holwerda, R. A. Gonzalez, Ronald J. Allen, P. C. Van Der Kruit

Faculty and Staff Scholarship

The "Synthetic Field Method" (SFM) was introduced by González et al. (1998, ApJ, 506, 152) to calibrate numbers of distant galaxies as a probe of extinction in a foreground spiral disk. González et al. (2003, AJ, 125, 1182) studied the effect of the foreground disk on these numbers using simulations of current and future instruments for fields in the LMC, M 31 and NGC 4536, a galaxy in Virgo. They concluded that: (1) the brighter centers of disks were unsuitable; (2) the granularity of the disk at a fixed surface brightness is the limiting factor in the detection of distant …

The Opacity Of Spiral Galaxy Disks. Vi. Extinction, Stellar Light And Color., Benne W. Holwerda, R. A. Gonzalez, P. C. Van Der Kruit, R. J. Allen

Faculty and Staff Scholarship

In this paper we explore the relation between dust extinction and stellar light distribution in disks of spiral galaxies. Extinction influences our dynamical and photometric perception of disks, since it can distort our measurement of the contribution of the stellar component. To characterize the total extinction by a foreground disk, González et al. (1998, ApJ, 506, 152) proposed the "Synthetic Field Method" (SFM), which uses the calibrated number of distant galaxies seen through the foreground disk as a direct indication of extinction. The method is described in González et al. (1998, ApJ, 506, 152) and Holwerda et al. (2005a, AJ, …

The First-Optical-Vla Survey For Lensed Radio Lobes, Deborah B. Haarsma, Joshua N. Winn, Emilio E. Falco, Christopher S. Kochanek

University Faculty Publications and Creative Works

We present results from a survey for gravitationally lensed radio lobes. Lensed lobes are a potentially richer source of information about galaxy mass distributions than lensed point sources, which have been the exclusive focus of other recent surveys. Our approach is to identify radio lobes in the Faint Images of the Radio Sky at Twenty cm (FIRST) catalog and then search optical catalogs for coincident foreground galaxies, which are candidate lensing galaxies. We then obtain higher resolution images of these targets at both optical and radio wavelengths and obtain optical spectra for the most promising candidates. We present maps of …

The Baryonic Tully-Fisher Relation Of Galaxies With Extended Rotation Curves And The Stellar Mass Of Rotating Galaxies, Stacy S. Mcgaugh

Faculty Scholarship

I investigate the baryonic Tully-Fisher relation for a sample of galaxies with extended 21 cm rotation curves spanning the range 20 km s-1 ≲ Vf ≤ 300 km s-1. A variety of scalings of the stellar mass-to-light ratio Υ* are considered. For each prescription for Υ*, I give fits of the form Md = AVfx. Presumably, the prescription that comes closest to the correct value will minimize the scatter in the relation. The fit with minimum scatter has A = 50 M⊙ km-4 s4 and x = 4. This relation holds over five decades in mass. Galaxy color, stellar fraction, …

The Opacity Of Spiral Galaxy Disks. Iii. Automating The Synthetic Field Method., Benne W. Holwerda, R. A. Gonzalez, Ronald J. Allen, P. C. Van Der Kruit

Faculty and Staff Scholarship

Dust extinction in spiral disks can be estimated from the counts of background field galaxies, provided the deleterious effects of confusion introduced by structure in the image of the foreground spiral disk can be calibrated. Gonzalez et al. developed a method for this calibration, the Synthetic Field Method (SFM), and applied this concept to a Hubble Space Telescope (HST )/Wide Field Planetary Camera 2 image of NGC 4536. The SFM estimates the total extinction through the disk without requiring assumptions about the distribution of absorbers or disk light. The poor statistics, however, result in large errors in individual measurements. We …

The Opacity Of Spiral Galaxy Disks. Iv. Radial Extinction Profiles From Counts Of Distant Galaxies Seen Through Foreground Disks., Benne W. Holwerda, R. A. Gonzalez, Ronald J. Allen, P. C. Van Der Kruit

Faculty and Staff Scholarship

Dust extinction can be determined from the number of distant field galaxies seen through a spiral disk. To calibrate this number for the crowding and confusion introduced by the foreground image, Gonzalez et al. and Holwerda et al. developed the Synthetic Field Method (SFM ), which analyzes synthetic fields constructed by adding various deep exposures of unobstructed background fields to the candidate foreground galaxy field. The advantage of the SFM is that it gives the average opacity for the area of a galaxy disk without making assumptions about either the distribution of absorbers or of the disk starlight. However, it …

The Mass Discrepancy-Acceleration Relation: Disk Mass And The Dark Matter Distribution, Stacy S. Mcgaugh

Faculty Scholarship

The mass discrepancy in disk galaxies is shown to be well correlated with acceleration, increasing systematically with decreasing acceleration below a critical scale a0 ≈ 3700 km2 s-2 kpc -1 = 1.2 × 10-10 m s-2. For each galaxy, there is an optimal choice of stellar mass-to-light ratio that minimizes the scatter in this mass discrepancy-acceleration relation. The same mass-to-light ratios also minimize the scatter in the baryonic Tully-Fisher relation and are in excellent agreement with the expectations of stellar population synthesis. Once the disk mass is determined in this fashion, the dark matter distribution is specified. The circular velocity …

The Baryonic Tully-Fisher Relation, Stacy S. Mcgaugh

Faculty Scholarship

We explore the Tully-Fisher relation over five decades in stellar mass in galaxies with circular velocities ranging over 30 ≲ Vc ≲ 300 km s-1. We find a clear break in the optical Tully-Fisher relation: field galaxies with Vc ≲ 90 km s-1 fall below the relation defined by brighter galaxies. These faint galaxies, however, are very rich in gas; adding in the gas mass and plotting the baryonic disk mass Md = M* + Mgas in place of luminosity restores the single linear relation. The Tully-Fisher relation thus appears fundamentally to be a relation between rotation velocity and total …

The Molecular Ism In Low Surface Brightness Disk Galaxies, J. Christopher Mihos, Stacy S. Mcgaugh

Faculty Scholarship

We present models for the interstellar medium in disk galaxies. In particular, we investigate whether the ISM in low surface brightness galaxies can support a significant fraction of molecular gas given their low metallicity and surface density. It is found that the abundance and line brightness of CO in LSB galaxies is small and typically below current observational limits. Still, depending on physical details of the ISM, the fraction of gas in the form of molecular hydrogen can be significant in the inner few kilo-parsecs of a low surface brightness galaxy. This molecular gas would be at temperatures of ∼ …

Testing Modified Newtonian Dynamics With Low Surface Brightness Galaxies: Rotation Curve Fits, Stacy S. Mcgaugh

Faculty Scholarship

We present modified Newtonian dynamics (MOND) fits to 15 rotation curves of low surface brightness (LSB) galaxies. Good fits are readily found, although for a few galaxies minor adjustments to the inclination are needed. Reasonable values for the stellar mass-to-light ratios are found, as well as an approximately constant value for the total (gas and stars) mass-to-light ratio. We show that the LSB galaxies investigated here lie on the one, unique Tully-Fisher relation, as predicted by MOND. The scatter on the Tully-Fisher relation can be completely explained by the observed scatter in the total mass-to-light ratio. We address the question …

Dynamical Stability And Environmental Influences In Low Surface Brightness Disk Galaxies, Stacy S. Mcgaugh

Faculty Scholarship

Using analytic stability criteria we demonstrate that, because of their low surface mass density and large dark matter content, low surface brightness (LSB) disks are quite stable against the growth of global nonaxisymmetric modes such as bars. However, depending on their (poorly constrained) stellar velocity dispersions, they may be only marginally stable against local instabilities. We simulate a collision between an LSB and a high surface brightness (HSB) galaxy and find that, while the HSB galaxy forms a strong bar, the response of the LSB disk is milder, manifesting weaker rings and spiral features. The lack of sufficient disk self-gravity …

Gas Mass Fractions And The Evolution Of Spiral Galaxies, Stacy S. Mcgaugh

Faculty Scholarship

We show that the gas mass fraction of spiral galaxies is strongly correlated with luminosity and surface brightness. It is not correlated with linear size. Gas fraction varies with luminosity and surface brightness at the same rate, indicating evolution at fixed size. Dim galaxies are clearly less evolved than bright ones, having consumed only ∼1/2 of their gas. This resolves the gas consumption paradox, since there exist many galaxies with large gas reservoirs. These gas-rich galaxies must have formed the bulk of their stellar populations in the last half of a Hubble time. The existence of such immature galaxies at …

Does Low Surface Brightness Mean Low Density?, Stacy S. Mcgaugh

Faculty Scholarship

We compare the dynamical properties of two galaxies at identical positions on the Tully-Fisher relation, but with different surface brightnesses. We find that the low surface brightness galaxy UGC 128 has a higher mass-to-light ratio, and yet has lower mass densities than the high surface brightness galaxy NGC 2403. This is true for the gas surface density, the stellar surface density, and the total mass density. © 1996. The American Astronomical Society. All rights reserved.

Imaging The Host Galaxies Of High-Redshift Radio-Quiet Qsos, James D. Lowenthal, Timothy M. Heckman, Matthew D. Lehnert, J. H. Elias

Astronomy: Faculty Publications

We present new deep K-band and optical images of four radio-quiet QSOs at z ≈ 1 and six radio-quiet QSOs at z ≈ 2.5, as well as optical images only of six more at z ≈ 2.5. We have examined the images carefully for evidence of extended "fuzz" from any putative QSO host galaxy. None of the z ≈ 2.5 QSOs shows any extended emission, and only two of the z ≈ 1 QSOs show marginal evidence for extended emission. Our 3 σ detection limits in the K images, mK ≃ 21 for an isolated source, would correspond approximately to …

Structural Characteristics And Stellar Composition Of Low Surface Brightness Disk Galaxies, Stacy S. Mcgaugh

Faculty Scholarship

We present UBVI surface photometry of a sample of low surface brightness (LSB) disk galaxies. LSB disk galaxies are fairly well described as exponential disks with no preferred value for either scale length, central surface brightness, or rotational velocity. Indeed, the distribution of scale lengths is indistinguishable from that of high surface brightness spirals, indicating that dynamically similar galaxies (e.g., those with comparable v2R) exist over a large range in surface density. These LSB galaxies are strikingly blue. The complete lack of correlation between central surface brightness and color rules out any fading scenario. Similarly, the oxygen abundances inferred from …

The Small Scale Environment Of Low Surface Brightness Disk Galaxies, Stacy S. Mcgaugh

Faculty Scholarship

We use a sample of ≈340 low surface brightness (LSB) disk galaxies with measured redshifts in combination with the Center for Astrophysics redshift survey to test the hypothesis that LSB galaxies have a deficit of nearby companion galaxies compared to high surface brightness (HSB) disk galaxies. We find a very strong statistical deficit of galaxies located within a projected radius of 0.5 Mpc and within a velocity of 500 km s-1 around LSB disk galaxies compared to HSB ones. Further, comparing LSB and HSB disk galaxies which are located in the same portion of the sky indicates that the average …