arXiv subjects

I. Puerari

Publications and source records attributed to I. Puerari.

At least 37 records · Page 2Linked to original sources

arXiv2011

The Bulgeless Seyfert/LINER Galaxy NGC 3367: Disk, Bar, Lopsidedness and Environment

NGC3367 is a nearby isolated active galaxy that shows a radio jet, a strong bar and evidence of lopsidedness. We present a quantitative analysis of the stellar and gaseous structure of the galaxy disk and a search for evidence of recent interaction based on new UBVRI Halpha and JHK images and on archival Halpha Fabry-Perot and HI VLA data. From a coupled 1D/2D GALFIT bulge/bar/disk decomposition an (B/D ~ 0.07-0.1) exponential pseudobulge is inferred in all the observed bands. A NIR estimate of the bar strength = 0.44 places NGC 3367 bar among the strongest ones. The asymmetry properties were studied using (1) optical and NIR CAS indexes (2) the stellar (NIR) and gaseous (Halpha, HI) A_1 Fourier mode amplitudes and (3) the HI integrated profile and HI mean intensity distribution. While the average stellar component shows asymmetry values close to the average found in the Local Universe for isolated galaxies, the young stellar component and gas values are largely decoupled showing significantly larger A_1 mode amplitudes suggesting that the gas has been recently perturbed. Our search for (1) faint stellar structures in the outer regions (up to u_R ~ 26 mag arcsec^{-2}), (2) (Halpha) star-forming satellite galaxies and (3) regions with different colors (stellar populations) along the disk all failed. Such an absence is interpreted using recent numerical simulations to constrain a tidal event with an LMC like galaxy to some dynamical times in the past or to a current very low mass, gas rich accretion. We conclude that a cold accretion mode (gas and small/dark galaxies) may be responsible of the nuclear activity and peculiar (young stars and gas) morphology regardless of the highly isolated environment. Black hole growth in bulgeless galaxies may be triggered by cosmic smooth mass accretion.

astro-ph.CO↗

arXiv2010

A Two-Component Power Law Covering Nearly Four Orders of Magnitude in the Power Spectrum of Spitzer Far-Infrared Emission from the Large Magellanic Cloud

Power spectra of Large Magellanic Cloud (LMC) emission at 24, 70 and 160 microns observed with the Spitzer Space Telescope have a two-component power-law structure with a shallow slope of -1.6 at low wavenumber, k, and a steep slope of -2.9 at high k. The break occurs at 1/k ~ 100-200 pc, which is interpreted as the line-of-sight thickness of the LMC disk. The slopes are slightly steeper for longer wavelengths, suggesting the cooler dust emission is smoother than the hot emission. The power spectrum covers ~ 3.5 orders of magnitude and the break in the slope is in the middle of this range on a logarithmic scale. Large-scale driving from galactic and extragalactic processes, including disk self-gravity, spiral waves and bars, presumably cause the low-k structure in what is effectively a two-dimensional geometry. Small-scale driving from stellar processes and shocks cause the high-k structure in a 3D geometry. This transition in dimensionality corresponds to the observed change in power spectrum slope. A companion paper models the observed power-law with a self-gravitating hydrodynamics simulation of a galaxy like the LMC.

astro-ph.CO↗

arXiv2009

Do Bars Drive Spiral Density Waves?

We present deep near-infrared K_s-band AAT IRIS2 observations of a selected sample of nearby barred spiral galaxies, including some with the strongest known bars. The sample covers a range of Hubble types from SB0- to SBc. The goal is to determine if the torque strengths of the spirals correlate with those of the bars, which might be expected if the bars actually drive the spirals as has been predicted by theoretical studies. This issue has implications for interpreting bar and spiral fractions at high redshift. Analysis of previous samples suggested that such a correlation exists in the near-infrared, where effects of extinction and star formation are less important. However, the earlier samples had only a few excessively strong bars. Our new sample largely confirms our previous studies, but still any correlation is relatively weak. We find two galaxies, NGC 7513 and UGC 10862, where there is a only a weak spiral in the presence of a very strong bar. We suggest that some spirals probably are driven by their bars at the same pattern speed, but that this may be only when the bar is growing or if there is abundant gas and dissipation.

astro-ph.CO↗

arXiv2006

The Building of Galactic Disks: Insights from the Triangulum Spiral Galaxy Messier 33

The Triangulum Spiral Galaxy Messier 33 offers unique insights into the building of a galactic disk. We identify spectacular arcs of intermediate age (0.6 Gyr - 2 Gyr) stars in the low-metallicity outer disk. The northern arc spans approx. 120 degrees in azimuth and up to 5 arcmin in width. The arcs are located 2-3 disk scale lengths from the galaxy centre (where 1 disk scale length is equivalent to 0.1 degrees in the V-band) and lie precisely where there is a warp in the HI profile of M33. Warps and infall are inextricably linked (Binney, 1992). We present spectroscopy of candidate stars in the outer northern arc, secured using the Keck I telescope in Hawaii. The target stars have estimated visual magnitudes as faint as V ~ 25m. Absorption bands of CN are seen in all spectra reported in this review talk, confirming their carbon star status. Also presented are PAH emissivity radial profiles generated from IRAC observations of M33 using the Spitzer Space Telescope. A dramatic change of phase in the m=2 Fourier component is detected at the domain of the arcs. M33 serves as an excellent example how the disks of spiral galaxies in our Universe are built: as dynamically open systems, growing from the inward, outward.

astro-ph↗

arXiv2005

Lopsided spiral galaxies: evidence for gas accretion

We quantify the degree of lopsidedness for a sample of 149 galaxies observed in the near-infrared from the OSUBGS sample, and try to explain the physical origin for the observed disk lopsidedness. We confirm previous studies, but now for a larger sample, that a large fraction of galaxies show significant lopsidedness in their stellar disks, measured as the Fourier amplitude of the m=1 component, normalised to the average or m=0 component, in the surface density. Late-type galaxies are found to be more lopsided, while the presence of m=2 spiral arms and bars is correlated. The m=1 amplitude is found to be uncorrelated with the tidal forces acting on a galaxy via nearby companions. Numerical simulations are carried out to study the generation of m=1 via different processes: galaxy tidal encounters, galaxy mergers, and external gas accretion and subsequent star formation. The simulations show that galaxy interactions and mergers can trigger strong lopsidedness, but do not explain several independent statistical properties of observed galaxies. To explain all the observational results, it is required that a large fraction of lopsidedness results from cosmological accretion of gas on galactic disks, which can create strongly lopsided disks when this accretion is asymmetrical enough.

astro-ph↗

arXiv2005

Dust Penetrated Arm Classes: Insights from rising and falling rotation curves

In the last decade, near-infrared imaging has highlighted the decoupling of gaseous and old stellar disks: the morphologies of optical (Population I) tracers compared to the old stellar disk morphology, can be radically different. Galaxies which appear multi-armed and even flocculent in the optical may show significant Grand-Design spirals in the near-infrared. Furthermore, the optically determined Hubble classification scheme does not provide a sound way of classifying dust-penetrated stellar disks: spiral arm pitch angles (when measured in the near-infrared) do not correlate with Hubble type. The dust--penetrated classification scheme of Block & Puerari provides an alternative classification based on near-infrared morphology, and which is thus more closely linked to the dominant stellar mass component. Here we present near--infrared K band images of 14 galaxies, on which we have performed a Fourier analysis of the spiral structure in order to determine their near-infrared pitch angles and dust--penetrated arm classes. We have also used the rotation curve data of Mathewson et al. to calculate the rates of shear in the stellar disks of these galaxies. We find a correlation between near-infrared pitch angle and rate of shear: galaxies with wide open arms (the $γ$ class) are found to have rising rotation curves, while those with falling rotation curves belong to the tightly wound $α$ bin. The major determinant of near-infrared spiral arm pitch angle is the distribution of matter within the galaxy concerned. The correlation reported in this study provides the physical basis underpinning spiral arm classes in the dust-penetrated regime and underscores earlier spectroscopic findings by Burstein and Rubin that Hubble type and mass distributions are unrelated.

astro-ph↗

arXiv2004

The Structural Properties of Isolated Galaxies, Spiral-Spiral Pairs, and Mergers: The Robustness of Galaxy Morphology During Secular Evolution

We present a structural analysis of nearby galaxies in spiral-spiral pairs in optical BVRI bands and compare with the structures of isolated spiral galaxies and galaxies in ongoing mergers. We use these comparisons to determine how galaxy structure changes during galaxy interactions and mergers. We analyze light concentration (C), asymmetry (A), and clumpiness (S) parameters, and use the projections of CAS parameter space to compare these samples. We find that the CAS parameters of paired galaxies are correlated with the projected separations of the pair. For the widest and closest pairs, the CAS parameters tend to be similar to those of isolated and ongoing major mergers (ULIRGs), respectively. Our results imply that galaxy CAS morphology is a robust quantity that only changes significantly during a strong interaction or major merger. The typical time-scale for this change in our paired sample, based on dynamical friction arguments, is short, t ~ 0.1 - 0.5 Gyr. We find average enhancement factors for the spiral pair asymmetries and clumpiness values of ~2.2 and 1.5. The S parameter, which is related to star formation activity, has a moderate level of enhancement suggesting that this activity in modern spirals depends more on internal processes than on external conditions. We furthermore test the statistical criterion for picking up interacting galaxies in an automated way by using the A-S projection plane. The diversity of our spiral pair sample in the CAS space suggests that structural/SF/morphological properties of interacting galaxies change abruptly only when the interaction becomes very strong and that the criteria for finding galaxies involved in major mergers from Conselice (2003) is effective.

astro-ph↗

arXiv2004

Very Luminous Carbon Stars in the Outer Disk of the Triangulum Spiral Galaxy

Stars with masses in the range from about 1.3 to 3.5 Mo pass through an evolutionary stage where they become carbon stars. In this stage, which lasts a few Myr, these stars are extremely luminous pulsating giants. They are so luminous in the near-infrared that just a few of them can double the integrated luminosity of intermediate-age (0.6 to 2 Gyr) Magellanic Cloud clusters at 2.2 microns. Astronomers routinely use such near-infrared observations to minimize the effects of dust extinction, but it is precisely in this band that carbon stars can contribute hugely. The actual contribution of carbon stars to the outer disk light of evolving spiral galaxies has not previously been morphologically investigated. Here we report new and very deep near-IR images of the Triangulum spiral galaxy M33=NGC 598, delineating spectacular arcs of carbon stars in its outer regions. It is these arcs which dominate the near-infrared m=2 Fourier spectra of M33. We present near-infrared photometry with the Hale 5-m reflector, and propose that the arcs are the signature of accretion of low metallicity gas in the outer disk of M33.

astro-ph↗

arXiv2004

Gravitational bar and spiral arm torques from K_s-band observations and implications for the pattern speeds

We have obtained deep near-infrared K_s-band William Herschel Telescope observations of a sample of 15 nearby spiral galaxies having a range of Hubble types and apparent bar strengths. The near-infrared light distributions are converted into gravitational potentials, and the maximum relative gravitational torques due to the bars and the spirals are estimated. We find that spiral strength, Q_s, and bar strength, Q_b, correlate well with other measures of spiral arm and bar amplitudes, and that spiral and bar strengths also correlate well with each other. We also find a correlation between the position angle of the end of the bar and the position angle of the inner spiral. These correlations suggest that the bars and spirals grow together with the same rates and pattern speeds. We also show that the strongest bars tend to have the most open spiral patterns. Because open spirals imply high disk-to-halo mass ratios, bars and spirals most likely grow together as a combined disk instability. They stop growing for different reasons, however, giving the observed variation in bar-spiral morphologies. Bar growth stops because of saturation when most of the inner disk is in the bar, and spiral growth stops because of increased stability as the gas leaves and the outer disk heats up.

astro-ph↗

arXiv2004

Probing Kolmogorov turbulence beyond the Magellanic Clouds: The Power of Southern Hemisphere's largest optical telescope (11m), SALT

The Hubble classification scheme of galaxies is based on blue-light appearance. Atlases reveal the rich variety of responses of the Population I component (`the mask') of gas and dust to the underlying, older, stellar population. However, the Population I component may only constitute 5 percent of the dynamical mass of the galaxy; furthermore, dusty masks are highly effective in hiding bars. We firstly discuss the rich duality in spiral structure, and highlight a near-infrared classification scheme for spiral galaxies. We next show that images secured with SALTICAM will be ideally suited to probe key questions such as whether the optical light in the gaseous Population I component is the result of Kolmogorov turbulence, cascasding from the largest of scales down to the Nyquist limit. If so, the optical emission in galaxies will be organized in a global fractal pattern with an intrinsic 1D power spectrum having a slope of -5/3, or -8/3 in 2D.

astro-ph↗

arXiv2002

The Link Between Rotation Curve Type and Spiral Arm Structure in Disk Galaxies

Over the last decade it has become clear that there is a decoupling between the old stellar disk and young stellar disk in spiral galaxies. This has led to a scheme for classifying galaxies on the basis of their near-infrared morphology. The near-infrared provides a more physical framework for classifying galaxies as it is both relatively free from extinction and it traces the old stellar population, i.e. the dominant stellar mass distribution. The `dust penetrated class' is dependent upon the spiral pitch angle of arms. We have observed 8 galaxies with UFTI on UKIRT in the K-band in order to investigate the theoretical link between disk dynamics and arm morphology, which is suggested both from numerical models and the dust penetrated class. We find that the pitch angle of spiral arms, i, correlates well with the shear rate of rotation curves, $A/ω$ (where A is the first Oort constant and $ω$ is the rotational velocity), over the same radial range.

astro-ph↗

arXiv2001

BVRI Surface Photometry of (S+S) Binary Galaxies. I. The data

We present multicolour broad band ($BVRI$) photometry for a sample of 33 spiral-spiral (S+S) binary galaxies drawn from the Karachentsev Catalogue of Isolated Pairs of Galaxies (KPG). The data is part of a joint observational programme devoted to systematic photometric study of one of the most complete and homogeneous pair samples available in the literature. We present azimuthally averaged colour and surface brightness profiles, colour index (B-I) maps, B band and sharp/filtered B band images as well as integrated magnitudes, magnitudes at different circular apertures and integrated colours for each pair. Internal and external data comparisons show consistency within the estimated errors. Two thirds of the sample have total aperture parameters homogeneously derived for the first time. After reevaluating morphology for all the pairs, we find a change in Hubble type for 24 galaxies compared to the original POSS classifications. More than half of our pairs show morphological concordance which could explain, in part, the strong correlation in the (B-V) colour indices (Holmberg Effect) between pair components. We find a tendency for barred galaxies to show grand design morphologies and flat colour profiles. The measurements will be used in a series of forthcoming papers where we try to identify and isolate the main structural and photometric properties of disk galaxies at different stages of interaction.

astro-ph↗

arXiv2001

Penetrating the Mask: The Gravitational Torque of Bars

The Hubble classification scheme of galaxies is based on blue-light appearance. Atlases reveal the rich variety of responses of the Population I component (the "mask") of gas and dust to the underlying, older, stellar population. However, the Population I component may only constitute 5 percent of the dynamical mass of the galaxy; furthermore, dusty masks are highly effective in hiding bars. In the 1960s, Ken Freeman presented a meticulous study of the dynamics of bars at a time when nonbarred galaxies were called "normal" spirals and barred galaxies were regarded as curiosities. Now we know that it is more "normal" for a galaxy to be barred than to be nonbarred. What is the range for gravitational torques of bars? We describe here a recently developed method for deriving relative bar torques by using gravitational potentials inferred from near-infrared light distributions. We incorporate a bar torque class into the Block/Puerari dust-penetrated galaxy classification system. We find a huge overlap in relative bar torque between Hubble (Sa, Sb, ...) and (SBa, SBb, ...) classifications. Application of the method to the high redshift universe is briefly discussed.

astro-ph↗

arXiv2001

Dust penetrated morphology in the high redshift Universe

Images from the Hubble Deep Field (HDF) North and South show a large percentage of dusty, high redshift galaxies whose appearance falls outside traditional classification systems. The nature of these objects is not yet fully understood. Since the HDF preferentially samples restframe UV light, HDF morphologies are not dust or `mask' penetrated. The appearance of high redshift galaxies at near-infrared restframes remains a challenge for the New Millennium. The Next Generation Space Telescope (NGST) could routinely provide us with such images. In this contribution, we quantitatively determine the dust-penetrated structures of high redshift galaxies such as NGC 922 in their near-infrared restframes. We show that such optically peculiar objects may readily be classified using the dust penetrated z ~ 0 templates of Block and Puerari (1999) and Buta and Block (2001).

astro-ph↗

arXiv2001

The gravitational torque of bars in optically unbarred and barred galaxies

The relative bar torques for 45 galaxies observed at $K$- band with the 4.2m William Herschel Telescope are determined by transforming the light distributions into potentials and deriving the maximum ratios of the tangential forces relative to the radial forces. The results are combined with the bar torques for 30 other galaxies determined from our previous $K$-band survey (Buta & Block 2001). Relative bar torques determine the degree of spiral arm forcing, gas accretion, and bar evolution. They differ from other measures of bar strength, such as the relative amplitude of the bar determined photometrically, because they include the bulge and other disk light that contributes to the radial component of the total force. If the bulge is strong and the radial forcing large, then even a prominent bar can have a relatively weak influence on the azimuthal motions in the disk. Here we find that the relative bar torque correlates only weakly with the optical bar type listed in the Revised Shapley-Ames and de Vaucouleurs systems. In fact, some classically barred galaxies have weaker relative bar torques than classically unbarred galaxies. The optical class is a poor measure of azimuthal disk forcing for two reasons: some infrared bars are not seen optically, and some bars with strong bulges have their azimuthal forces so strongly diluted by the average radial force that they exert only small torques on their disks. The Hubble classification scheme poorly recognizes the gravitational influence of bars. Applications of our bar torque method to the high-redshift universe are briefly discussed.

astro-ph↗

arXiv2001

Dust-penetrated morphology in the high-redshift universe: clues from NGC 922

Results from the Hubble Deep Field (HDF) North and South show a large percentage of high-redshift galaxies whose appearance falls outside traditional classification systems. The nature of these objects is poorly understood, but sub-mm observations indicate that at least some of these systems are heavily obscured (Sanders 2000). This raises the intriguing possibility that a physically meaningful classification system for high-redshift galaxies might be more easily devised at rest-frame infrared wavelengths, rather than in the optical regime. Practical realization of this idea will become possible with the advent of the Next Generation Space Telescope (NGST). In order to explore the capability of NGST for undertaking such science, we present NASA-IRTF and SCUBA observations of NGC 922, a chaotic system in our local Universe which bears a striking resemblance to objects such as HDF 2-86 (z=0.749) in the HDF North. If objects such as NGC 922 are common at high-redshifts, then this galaxy may serve as a local morphological `Rosetta stone' bridging low and high-redshift populations. In this paper we demonstrate that quantitative measures of galactic structure are recoverable in the rest-frame infrared for NGC 922 seen at high redshifts using NGST, by simulating the appearance of this galaxy at redshifts z=0.7 and z=1.2 in rest-frame K'. Our results suggest that the capability of efficiently exploring the rest-wavelength IR morphology of high-z galaxies should probably be a key factor in deciding the final choice of instruments for the NGST.

astro-ph↗

arXiv2001

The Duality of Spiral Structure, and a Quantitative Dust Penetrated Morphological Tuning Fork at Low and High Redshift

In the near-infrared, the morphology of older star-dominated disks indicates a simple classification scheme (1) H$m$ where $m$ is the dominant harmonic, (2) a pitch angle (derived from the Fourier spectra) associated with the rate of shear A/$ω$ in the stellar disk and (3) a `bar strength' parameter, robustly derived from the gravitational potential or torque of the bar. A spiral galaxy may present two radically different morphologies in the optical and near-infrared regime; there is no correlation between our quantitative dust penetrated tuning fork and that of Hubble. Applications of our $z\sim$0 Fourier template to the HDF are discussed using $L$ and $M$ band simulations from an 8-m NGST; the rest-wavelength IR morphology of high-$z$ galaxies should probably be a key factor in deciding the final choice of instruments for the NGST.

astro-ph↗

arXiv1999

Formation of massive counter-rotating disks: an alternative scenario

In this contribution, we investigate the scenario of major mergers between galaxies of comparable mass to the formation of massive counter-rotating disks. Such a scenario can be ruled out in general because they produce rather ellipticals. Yet for a narrow range of initial conditions, major mergers can nevertheless produce anyway rare galaxies such as NGC 4550, and so they are viable alternatives for the formation of these counter-rotating systems. The scenario is successful in producing a remarkably axisymmetric disk possessing strongly counter-rotating populations.

astro-ph↗