arXiv subjects

D. A. Gadotti

Publications and source records attributed to D. A. Gadotti.

49 records · Page 3Linked to original sources

arXiv2015

The Spitzer Survey of Stellar Structure in Galaxies (S$^4$G): Precise Stellar Mass Distributions from Automated Dust Correction at 3.6 microns

The mid-infrared is an optimal window to trace stellar mass in nearby galaxies and the 3.6$μm$ IRAC band has been exploited to this effect, but such mass estimates can be biased by dust emission. We present our pipeline to reveal the old stellar flux at 3.6$μm$ and obtain stellar mass maps for more than 1600 galaxies available from the Spitzer Survey of Stellar Structure in Galaxies (S$^{4}$G). This survey consists of images in two infrared bands (3.6 and 4.5$μm$), and we use the Independent Component Analysis (ICA) method presented in Meidt et al. (2012) to separate the dominant light from old stars and the dust emission that can significantly contribute to the observed 3.6$μm$ flux. We exclude from our ICA analysis galaxies with low signal-to-noise ratio (S/N < 10) and those with original [3.6]-[4.5] colors compatible with an old stellar population, indicative of little dust emission (mostly early Hubble types, which can directly provide good mass maps). For the remaining 1251 galaxies to which ICA was successfully applied, we find that as much as 10-30% of the total light at 3.6$μm$ typically originates from dust, and locally it can reach even higher values. This contamination fraction shows a correlation with specific star formation rates, confirming that the dust emission that we detect is related to star formation. Additionally, we have used our large sample of mass estimates to calibrate a relationship of effective mass-to-light ratio ($M/L$) as a function of observed [3.6]-[4.5] color: $\log(M/L)=-0.339 (\pm 0.057) \times ([3.6]-[4.5]) -0.336 (\pm 0.002)$. Our final pipeline products have been made public through IRSA, providing the astronomical community with an unprecedentedly large set of stellar mass maps ready to use for scientific applications.

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arXiv2014

The Baryonic Tully-Fisher Relationship for S$^4$G Galaxies and the "Condensed" Baryon Fraction of Galaxies

We combine data from the Spitzer Survey for Stellar Structure in Galaxies (S$^4$G), a recently calibrated empirical stellar mass estimator from Eskew et al., and an extensive database of HI spectral line profiles to examine the baryonic Tully-Fisher (BTF) relation. We find 1) that the BTF has lower scatter than the classic Tully-Fisher (TF) relation and is better described as a linear relationship, confirming similar previous results, 2) that the inclusion of a radial scale in the BTF decreases the scatter but only modestly, as seen previously for the TF relation, and 3) that the slope of the BTF, which we find to be $3.5\pm 0.2$ ($Δ$ log $M_{baryon}/Δ$ log $v_c$), implies that on average a nearly constant fraction ($\sim 0.4$) of all baryons expected to be in a halo are "condensed" onto the central region of rotationally supported galaxies. The condensed baryon fraction, $M_{baryon}/M_{total}$, is, to our measurement precision, nearly independent of galaxy circular velocity (our sample spans circular velocities, $v_c$, between 60 and 250 km s$^{-1}$, but is extended to $v_c\sim 10$ km s$^{-1}$ using data from the literature). The observed galaxy-to-galaxy scatter in this fraction is generally $\le$ a factor of 2 despite fairly liberal selection criteria. These results imply that cooling and heating processes, such as cold vs. hot accretion, mass loss due to stellar winds, and AGN driven feedback, to the degree that they affect the global galactic properties involved in the BTF, are independent of halo mass for galaxies with $10 < v_c < 250$ km/s and typically introduce no more than a factor of two range in the resulting $M_{baryon}/M_{total}$. Recent simulations by Aumer et al. of a small sample of disk galaxies are in excellent agreement with our data, suggesting that current simulations are capable of reproducing the global properties of individual disk galaxies.

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arXiv2014

Reconstructing the stellar mass distributions of galaxies using S4G IRAC 3.6 and 4.5 micron images: II. The conversion from light to mass

We present a new approach for estimating the 3.6 micron stellar mass-to-light ratio in terms of the [3.6]-[4.5] colors of old stellar populations. Our approach avoids several of the largest sources of uncertainty in existing techniques. By focusing on mid-IR wavelengths, we gain a virtually dust extinction-free tracer of the old stars, avoiding the need to adopt a dust model to correctly interpret optical or optical/NIR colors normally leveraged to assign M/L. By calibrating a new relation between NIR and mid-IR colors of GLIMPSE giant stars we also avoid discrepancies in model predictions for the [3.6]-[4.5] colors of old stellar populations due to uncertainties in molecular line opacities. We find that the [3.6]-[4.5] color, which is driven primarily by metallicity, provides a tight constraint on M/L_3.6, which varies intrinsically less than at optical wavelengths. The uncertainty on M/L_3.6 of ~0.07 dex due to unconstrained age variations marks a significant improvement on existing techniques for estimating the stellar M/L with shorter wavelength data. A single M/L_3.6=0.6 (assuming a Chabrier IMF), independent of [3.6]-[4.5] color, is also feasible as it can be applied simultaneously to old, metal-rich and young, metal-poor populations, and still with comparable (or better) accuracy (~0.1 dex) as alternatives. We expect our M/L_3.6 to be optimal for mapping the stellar mass distributions in S4G galaxies, for which we have developed an Independent Component Analysis technique to first isolate the old stellar light at 3.6 micron from non-stellar emission (e.g. hot dust and the 3.3 PAH feature). Our estimate can also be used to determine the fractional contribution of non-stellar emission to global (rest-frame) 3.6 micron fluxes, e.g. in WISE imaging, and establishes a reliable basis for exploring variations in the stellar IMF.

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arXiv2013

Morphological Parameters of Spitzer Survey of Stellar Structure in Galaxies (S4G)

The morphology of galaxies can be quantified to some degree using a set of scale-invariant parameters. Concentration (C), Asymmetry (A), Smoothness (S), the Gini index (G), relative contribution of the brightest pixels to the second order moment of the flux (M20), ellipticity (E), and the Gini index of the second order moment (GM) have all been applied to morphologically classify galaxies at various wavelengths. Here we present a catalog of these parameters for the Spitzer Survey of Stellar Structure in Galaxies (S4G), a volume-limited near-infrared imaging survey of nearby galaxies using the 3.6 and 4.5 micron channels of the IRAC camera. Our goal is to provide a reference catalog of near-infrared quantified morphology for high-redshift studies and galaxy evolution models with enough detail to resolve stellar mass morphology. We explore where normal, non-interacting galaxies -those typically found on the Hubble tuning fork- lie in this parameter space and show that there is a tight relation between Concentration and M20 for normal galaxies. M20 can be used to classify galaxies into earlier and later types (e.g., to separate spirals from irregulars). Several criteria using these parameters exist to select systems with a disturbed morphology, i.e., those that appear to be undergoing a tidal interaction. We examine the applicability of these criteria to Spitzer near-infrared imaging. We find that four relations, based on the parameters A&S, G&M20, GM, and C&M20, respectively, select outliers in the morphological parameter space, but each selects different subsets of galaxies. Two criteria (GM > 0.6, G > -0.115 x M20 + 0.384) seem most appropriate to identify possible mergers and the merger fraction in near-infrared surveys. We find no strong relation between lopsidedness and most of these morphological parameters, except for a weak dependence of lopsidedness on Concentration and M20.

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arXiv2013

The impact of bars on disk breaks as probed by S4G imaging

We have analyzed the radial distribution of old stars in a sample of 218 nearby face-on disks, using deep 3.6um images from the Spitzer Survey of Stellar Structure in Galaxies (S4G). In particular, we have studied the structural properties of those disks with a broken or down-bending profile. We find that, on average, disks with a genuine single exponential profile have a scale-length and a central surface brightness which are intermediate to those of the inner and outer components of a down-bending disk with the same total stellar mass. In the case of barred galaxies, the ratio between the break and the bar radii (Rbr/Rbar) depends strongly on the total stellar mass of the galaxy. For galaxies more massive than 10^10 Msun, the distribution is bimodal, peaking at Rbr/Rbar~2 and ~3.5. The first peak, which is the most populated one, is linked to the Outer Lindblad Resonance of the bar, whereas the second one is consistent with a dynamical coupling between the bar and the spiral pattern. For galaxies below 10^10 Msun, breaks are found up to ~10 Rbar, but we show that they could still be caused by resonances given the rising nature of rotation curves in these low-mass disks. While not ruling out star formation thresholds, our results imply that radial stellar migration induced by non-axysymmetric features can be responsible not only for those breaks at 2 Rbar, but also for many of those found at larger radii.

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arXiv2011

Looking inside the nest: the hidden structure of the merger galaxy NGC 1316 (Fornax A)

We present an analysis of the circumnuclear structure of NGC 1316 using both near-infrared imaging and stellar kinematics. 2D decomposition of the images suggests the presence of a structure that resembles inner gaseous spiral arms, at about 5 to 15" from the center (500 to 1500 pc). We also find a disc-like stellar structure with radius less than 200 pc. Analysis of previously published SINFONI integral field kinematics data indicates a kinematically decoupled core in the same spatial scale, further evidence that indeed the nuclear stellar structure found is a kinematically cold stellar disc. We suggest that both newly-found structural components are the result of a recent accretion of a companion galaxy.

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arXiv2010

The Herschel-ATLAS: The dust energy balance in the edge-on spiral galaxy UGC 4754

We use Herschel PACS and SPIRE observations of the edge-on spiral galaxy UGC 4754, taken as part of the H-ATLAS SDP observations, to investigate the dust energy balance in this galaxy. We build detailed SKIRT radiative models based on SDSS and UKIDSS maps and use these models to predict the far-infrared emission. We find that our radiative transfer model underestimates the observed FIR emission by a factor of two to three. Similar discrepancies have been found for other edge-on spiral galaxies based on IRAS, ISO, and SCUBA data. Thanks to the good sampling of the SED at FIR wavelengths, we can rule out an underestimation of the FIR emissivity as the cause for this discrepancy. Instead we support highly obscured star formation that contributes little to the optical extinction as a more probable explanation.

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arXiv2009

Kinematic properties as probes of the evolution of dwarf galaxies in the Virgo cluster

We present new observational results on the kinematical, morphological, and stellar population properties of a sample of 21 dEs located both in the Virgo cluster and in the field, which show that 52% of the dEs i) are rotationally supported, ii) exhibit structural signs of typical rotating systems such as discs, bars or spiral arms, iii) are younger (~3 Gyr) than non-rotating dEs, and iv) are preferentially located either in the outskirts of Virgo or in the field. This evidence is consistent with the idea that rotationally supported dwarfs are late type spirals or irregulars that recently entered the cluster and lost their gas through a ram pressure stripping event, quenching their star formation and becoming dEs through passive evolution. We also find that all, but one, galaxies without photometric hints for hosting discs are pressure supported and are all situated in the inner regions of the cluster. This suggests a different evolution from the rotationally supported systems. Three different scenarios for these non-rotating galaxies are discussed (in situ formation, harassment and ram pressure stripping).

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arXiv2009

Comparing photometric results of real and N-body bars

We compare the results of the photometrical analysis of barred galaxies with those of a similar analysis from N-body simulations. The photometry is for a sample of nine barred galaxies observed in the J and Ks bands with the CANICA near infrared (NIR) camera at the 2.1-m telescope of the Observatorio Astrofisico Guillermo Haro (OAGH) in Cananea, Sonora, Mexico. The comparison includes radial ellipticity profiles and surface brightness (density for the N-body galaxies) profiles along the bar major and minor axes. We find very good agreement, arguing that the exchange of angular momentum within the galaxy plays a determinant role in the evolution of barred galaxies.

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arXiv2005

Dating Secular Evolution: Bar Ages from Stellar Kinematics

The last few years witnessed a change of perspective in the context of galaxy formation and evolution. The major role played by bars in the history of these fundamental building blocks of our universe was finally realized. However, and despite the fact that one of the major concerns of any physical science is to measure timescales for natural phenomena, we have as yet no established way to estimate the ages of these important galactic components. In this contribution we outline the method we developed to estimate bar ages and briefly describe its first results.

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arXiv2004

BUDDA: A New Two-Dimensional Bulge/Disk Decomposition Code for Detailed Structural Analysis of Galaxies

We present BUDDA (BUlge/Disk Decomposition Analysis), a new code devoted to perform a two-dimensional bulge/disk decomposition directly from the images of galaxies. The bulge component is fitted with a generalized Sersic profile whereas disks have an exponential profile. No other components are included. Bars and other sub-structures, like lenses, rings, inner bars and inner disks, are studied with the residual images obtained through the subtraction of bulges and disks from the original images. This means that a detailed structural analysis of galaxies may be performed with a small number of parameters, and sub-structures may be directly studied with no a priori assumptions. To illustrate its usefulness, we present the results obtained with a sample of 51 mostly early-type galaxies (but covering the whole Hubble sequence). These results show some of the applications in which the code may be used: the determination of parameters for Fundamental Plane and structural studies, quantitative morphological classification of galaxies and identification and study of hidden sub-structures. We have determined the structural parameters of the galaxies in our sample and found many examples of hidden inner disks in ellipticals, secondary bars, nuclear rings and dust lanes in lenticulars and spirals, and also wrong morphological classification cases.

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arXiv2003

NGC 4608 and NGC 5701: Barred Galaxies without Disks?

We have performed for the first time in the literature a 2D structural analysis on the barred lenticular and face--on galaxies NGC 4608 and NGC 5701. The results indicate that these galaxies either have never had large disks or their disks were almost completely destroyed by their strong bars, due to secular evolution processes. We discuss these surprising conclusions checking for signs of secular evolution, considering bar forming instabilities, and suggesting, based on N-body simulations, a new mechanism to form bars in spheroids, which includes non-spherical halos. Quantitative predictions from our new mechanism are compared with those from other recent models for bar formation and evolution.

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arXiv2000

Stellar Populations, Bars and Secular Evolution in Late-Type Galaxies

We have done a robust statistical analysis of UBV color profiles of 257 Sbc barred and unbarred galaxies. We found that there is an excess of barred galaxies among the objects with null or positive (bluish inward) color gradients, which seems to indicate that bars act as a mechanism of homogenization of the stellar population along galaxies. Moreover, the relationship found between total and bulge colors shows that, in the process of homogenization, the stellar population of bulges are getting bluer, whereas the total color of galaxies remains the same. These characteristics are expected in a secular evolutionary scenario, and seem incompatible with both the monolithic and the hierarchical scenarios for spiral galaxy formation.

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