The Intrinsic Shape of Spiral Galaxies in the 2MASS Large Galaxy Atlas

Ryden, Barbara S.

doi:10.1086/500497

Cited by 42 publications

(64 citation statements)

References 40 publications

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“…The existence of two populations of Ne/O, rather than simply a large spread in a single population, is confirmed using a nonparametric kernel technique that does not presuppose an a priori shape to the distribution (Vio et al 1994;Ryden 2006). Hii regions that exhibit low Ne/O do not display unusual deficits in other relative .…”

Section: Enrichment Relative To Oxygen Inmentioning

confidence: 83%

Chaos. Iii. Gas-Phase Abundances in NGC 5457

Croxall

Pogge

Berg

et al. 2016

ApJ

133

150

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The CHemical Abundances of Spirals (CHAOS) project leverages the combined power of the Large Binocular Telescope (LBT) with the broad spectral range and sensitivity of the Multi Object Double Spectrograph (MODS) to measure "direct" abundances (based on observations of the temperaturesensitive auroral lines) in large samples of H II regions in spiral galaxies. λ4076 at a strength of ≥ 3 σ), a factor of ∼3 larger than all previous published detections of auroral lines in the Hii regions of NGC 5457. Comparing the temperatures derived from the different ionic species we find: (1) correlations of T[N ii] with T[S iii] and T[O iii] match the predictions of photoionization modeling while the correlation of T[S iii] with T[O iii]is offset from the prediction of photoionization modeling. Based on these observations, which include significantly more observations of lower excitation Hii regions, missing in many analyses, we inspect the commonly used ionization correction factors (ICFs) for unobserved ionic species and propose new empirical ICFs for S and Ar. We have discovered an unexpected population of H II regions with a significant offset to low values in Ne/O, which defies explanation. We derive radial gradients in O/H and N/O which agree with previous studies. Our large observational database allows us to examine the dispersion in abundances, and we find intrinsic dispersions of 0.074 ± 0.009 in O/H and 0.095 ± 0.009 in N/O (at a given radius). We stress that this measurement of the intrinsic dispersion comes exclusively from direct measurements of Hii regions in NGC 5457.

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Section: Enrichment Relative To Oxygen Inmentioning

confidence: 83%

Chaos. Iii. Gas-Phase Abundances in NGC 5457

Croxall

Pogge

Berg

et al. 2016

ApJ

133

150

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“…As for the flattening, the intrinsic ellipticity depends on the morphological type and wavelength. The disks of early-type spirals are more elliptical than those of late-type spirals and their median ellipticity increases with observed wavelength (Ryden 2006). Furthermore, luminous spiral galaxies tend to have thicker and rounder disks than lowluminosity spiral galaxies (Padilla & Strauss 2008).…”

Section: Intrinsic Shape Of Disk Galaxiesmentioning

confidence: 94%

Structural properties of disk galaxies

Méndez-Abreu

Simonneau

Aguerri

et al. 2010

A&A

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Context. Knowledge of the intrinsic shapes of galaxy components provides crucial information when constraining phenomena driving their formation and evolution. Aims. We analize the structural parameters of a magnitude-limited sample of 148 unbarred S0-Sb galaxies to derive the intrinsic shape of their bulges. Methods. We developed a new method to derive the intrinsic shapes of bulges based on geometrical relationships between the apparent and intrinsic shapes of bulges and disks. Bulges were assumed to be triaxial ellipsoids sharing the same center and polar axis of their surrounding disks. Disks were assumed to be circular, infinitesimally thin, and to lie on the equatorial plane of bulges. The equatorial ellipticity and intrinsic flattening of bulges were obtained from the length of the apparent major and minor semi-axes of the bulge, the twist angle between the apparent major axis of the bulge and the galaxy line of nodes, and the galaxy inclination. Results. We find that the intrinsic shape is well constrained for a subsample of 115 bulges with favorable viewing angles. A large fraction of them are characterized by an elliptical section (B/A < 0.9). This fraction is 33%, 55%, and 43% if using their maximum, mean, or median equatorial ellipticity, respectively. Most are flattened along their polar axis (C < (A + B)/2). Only 18% of the observed bulges have a probability >50% and none has a probability >90% of being elongated along the polar axis. The distribution of triaxiality is strongly bimodal. This bimodality is driven by bulges with Sérsic index n > 2, or equivalently, by the bulges of galaxies with a bulge-to-total ratio B/T > 0.3. Bulges with n ≤ 2 and with B/T ≤ 0.3 follow a similar distribution, which differs from that of bulges with n > 2 and B/T > 0.3. In particular, bulges with n ≤ 2 and B/T ≤ 0.3 exhibit a larger fraction of oblate axisymmetric (or nearly axisymmetric) bulges, a smaller fraction of triaxial bulges, and fewer prolate axisymmetric (or nearly axisymmetric) bulges with respect to bulges with n > 2 and with B/T > 0.3, respectively. No correlation is found between the intrinsic shape and either the luminosity or velocity dispersion of bulges. Conclusions. According to predictions of the numerical simulations of bulge formation, bulges with n ≤ 2, which show a high fraction of oblate axisymmetric (or nearly axisymmetric) shapes and have B/T ≤ 0.3, may be the result of dissipational minor mergers. Both major dissipational and dissipationless mergers seem to be required to explain the variety of shapes found for bulges with n > 2 and B/T > 0.3.

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“…The intrinsic ellipticities of disks, thought to be $5%Y10% rms depending on galaxy type and band (Rix & Zaritsky 1995;Ryden 2006), are an irreducible source of uncertainty in TF studies without two-dimensional velocity fields, since they prevent one from perfectly measuring a galaxy's inclination and thus inferring its deprojected rotation speed. We have selected galaxies to have a measured axis ratio b/a 0:6, so that a 5% intrinsic ellipticity would change the inclination-corrected rotation velocity V obs /sin i / V obs (1 À b 2 /a 2 ) À1/2 by 5%.…”

Section: Sdss Observations and Sample Selectionmentioning

confidence: 99%

“…We thus implicitly assume that the disk is adequately described by a circularly symmetric exponential, and disk ellipticities by definition contribute to the intrinsic rather than the observational scatter. Rix & Zaritsky (1995), from a study of face-on galaxies, estimated typical ellipticities of $0.05 for the gravitational potential in the disk plane, which would cause $0.15 mag of TF scatter from a combination of inclination-correction errors and noncircular motions (see also Franx & de Zeeuw 1992;Ryden 2006). …”

Section: Intrinsic Scattermentioning

confidence: 99%

The Tully-Fisher Relation and its Residuals for a Broadly Selected Sample of Galaxies

et al. 2007

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We measure the relation between galaxy luminosity and disk circular velocity (the Tully-Fisher [TF] relation), in the g, r, i, and z bands, for a broadly selected sample of galaxies from the Sloan Digital Sky Survey, with the goal of providing well-defined observational constraints for theoretical models of galaxy formation. The input sample of 234 galaxies has a roughly flat distribution of absolute magnitudes in the range À18:5 > M r > À22, and our only morphological selection is an isophotal axis ratio cut b/a < 0:6 to allow accurate inclination corrections. Long-slit spectroscopy from the Calar Alto and MDM observatories yields usable H rotation curves for 162 galaxies (69%), with a representative color and morphology distribution. We define circular velocities V 80 by evaluating the rotation curve at the radius containing 80% of the i-band light. Observational errors, including estimated distance errors due to peculiar velocities, are small compared to the intrinsic scatter of the TF relation. The slope of the forward TF relation steepens from À5:5 AE 0:2 mag ( log 10 km s À1 ) À1 in the g band to À6:6 AE 0:2 mag ( log 10 km s À1 ) À1 in the z band. The intrinsic scatter is % 0:4 mag in all bands, and residuals from either the forward or inverse relations have an approximately Gaussian distribution. We discuss how Malmquist-type biases may affect the observed slope, intercept, and scatter. The scatter is not dominated by rare outliers or by any particular class of galaxies, although it drops slightly, to % 0:36 mag, if we restrict the sample to nearly bulgeless systems. Correlations of TF residuals with other galaxy properties are weak: bluer galaxies are significantly brighter than average in the g-band TF relation but only marginally brighter in the i band; more concentrated (earlier type) galaxies are slightly fainter than average, and the TF residual is virtually independent of half-light radius, contrary to the trend expected for gravitationally dominant disks. The observed residual correlations do not account for most of the intrinsic scatter, implying that this scatter is instead driven largely by variations in the ratio of dark to luminous matter within the disk galaxy population.

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The Intrinsic Shape of Spiral Galaxies in the 2MASS Large Galaxy Atlas

Cited by 42 publications

References 40 publications

Chaos. Iii. Gas-Phase Abundances in NGC 5457

Chaos. Iii. Gas-Phase Abundances in NGC 5457

Structural properties of disk galaxies

The Tully-Fisher Relation and its Residuals for a Broadly Selected Sample of Galaxies

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