GLOBULAR CLUSTER POPULATIONS: RESULTS INCLUDING S⁴G LATE-TYPE GALAXIES

Zaritsky, Dennis,McCabe, Kelsey,Aravena, Manuel,Athanassoula, E.,Bosma, Albert,Comeró,n, Sé,bastien,Courtois, Helene M.,Elmegreen, Bruce G.,Elmegreen, Debra M.,Erroz-Ferrer, Santiago,Gadot American Astronomical Society 2016 The Astrophysical journal Vol.818 No.1

<P>Using 3.6 and 4.5 mu m images of 73 late-type, edge-on galaxies from the S(4)G survey, we compare the richness of the globular cluster populations of these galaxies to those of early-type galaxies that we measured previously. In general, the galaxies presented here fill in the distribution for galaxies with lower stellar mass, M-*, specifically log(M-*/M-circle dot) < 10, overlap the results for early-type galaxies of similar masses, and, by doing so, strengthen the case for a dependence of the number of globular clusters per 10(9)M(circle dot) of galaxy stellar mass, T-N, on M-*. For 8.5 < log(M-*/M-circle dot) < 10.5 we find the relationship can be satisfactorily described as T-N = (M-*/10(6.7))(-0.56) M-* is expressed in solar masses. The functional form of the relationship is only weakly constrained, and extrapolation outside this range is not advised. Our late-type galaxies, in contrast to our early types, do not show the tendency for low-mass galaxies to split into two T-N families. Using these results and a galaxy stellar mass function from the literature, we calculate that, in a volume-limited, local universe sample, clusters are most likely to be found around fairly massive galaxies (M-* similar to 10(10.8)M(circle dot)) and present a fitting function for the volume number density of clusters as a function of parent-galaxy stellar mass. We find no correlation between T-N and large-scale environment, but we do find a tendency for galaxies of fixed M-* to have larger T-N if they have converted a larger proportion of their baryons into stars.</P>

RECONSTRUCTING THE STELLAR MASS DISTRIBUTIONS OF GALAXIES USING S⁴G IRAC 3.6 AND 4.5 μm IMAGES. I. CORRECTING FOR CONTAMINATION BY POLYCYCLIC AROMATIC HYDROCARBONS, HOT DUST, AND INTERMEDIATE-AGE STARS

Meidt, Sharon E.,Schinnerer, Eva,Knapen, Johan H.,Bosma, Albert,Athanassoula, E.,Sheth, Kartik,Buta, Ronald J.,Zaritsky, Dennis,Laurikainen, Eija,Elmegreen, Debra,Elmegreen, Bruce G.,Gadotti, Dimitri IOP Publishing 2012 The Astrophysical journal Vol.744 No.1

<P>With the aim of constructing accurate two-dimensional maps of the stellar mass distribution in nearby galaxies from Spitzer Survey of Stellar Structure in Galaxies 3.6 and 4.5 mu m images, we report on the separation of the light from old stars from the emission contributed by contaminants. Results for a small sample of six disk galaxies (NGC 1566, NGC 2976, NGC 3031, NGC 3184, NGC 4321, and NGC 5194) with a range of morphological properties, dust content, and star formation histories are presented to demonstrate our approach. To isolate the old stellar light from contaminant emission (e.g., hot dust and the 3.3 mu m polycyclic aromatic hydrocarbon (PAH) feature) in the IRAC 3.6 and 4.5 mu m bands we use an independent component analysis (ICA) technique designed to separate statistically independent source distributions, maximizing the distinction in the [3.6]-[4.5] colors of the sources. The technique also removes emission from evolved red objects with a low mass-to-light ratio, such as asymptotic giant branch (AGB) and red supergiant (RSG) stars, revealing maps of the underlying old distribution of light with [3.6]-[4.5] colors consistent with the colors of K and M giants. The contaminants are studied by comparison with the non-stellar emission imaged at 8 mu m, which is dominated by the broad PAH feature. Using the measured 3.6 mu m/8 mu m ratio to select individual contaminants, we find that hot dust and PAHs together contribute between similar to 5% and 15% to the integrated light at 3.6 mu m, while light from regions dominated by intermediate-age (AGB and RSG) stars accounts for only 1%-5%. Locally, however, the contribution from either contaminant can reach much higher levels; dust contributes on average 22% to the emission in star-forming regions throughout the sample, while intermediate-age stars contribute upward of 50% in localized knots. The removal of these contaminants with ICA leaves maps of the old stellar disk that retain a high degree of structural information and are ideally suited for tracing stellar mass, as will be the focus in a companion paper.</P>

Nuclear Spiral Shocks and Induced Gas Inflows in Weak Oval Potentials

Kim, Woong-Tae,Elmegreen, Bruce G. American Astronomical Society 2017 ASTROPHYSICAL JOURNAL LETTERS - Vol.841 No.1

<P>Nuclear spirals are ubiquitous in galaxy centers. They exist not only in strong barred galaxies but also in galaxies without noticeable bars. We use high-resolution hydrodynamic simulations to study the properties of nuclear gas spirals driven by weak bar-like and oval potentials. The amplitude of the spirals increases toward the center by a geometric effect, readily developing into shocks at small radii even for very weak potentials. The shape of the spirals and shocks depends rather sensitively on the background shear. When shear is low, the nuclear spirals are loosely wound and the shocks are almost straight, resulting in large mass inflows toward the center. When shear is high, on the other hand, the spirals are tightly wound and the shocks are oblique, forming a circumnuclear disk through which gas flows inward at a relatively lower rate. The induced mass inflow rates are enough to power black hole accretion in various types of Seyfert galaxies as well as to drive supersonic turbulence at small radii.</P>

THICK DISKS OF EDGE-ON GALAXIES SEEN THROUGH THE<i>SPITZER</i>SURVEY OF STELLAR STRUCTURE IN GALAXIES (S⁴G): LAIR OF MISSING BARYONS?

Comeró,n, Sé,bastien,Elmegreen, Bruce G.,Knapen, Johan H.,Salo, Heikki,Laurikainen, Eija,Laine, Jarkko,Athanassoula, E.,Bosma, Albert,Sheth, Kartik,Regan, Michael W.,Hinz, Joannah L.,de Pa IOP Publishing 2011 The Astrophysical journal Vol.741 No.1

<P>Most, if not all, disk galaxies have a thin (classical) disk and a thick disk. In most models thick disks are thought to be a necessary consequence of the disk formation and/or evolution of the galaxy. We present the results of a study of the thick disk properties in a sample of carefully selected edge-on galaxies with types ranging from T = 3 to T = 8. We fitted one-dimensional luminosity profiles with physically motivated functions-the solutions of two stellar and one gaseous isothermal coupled disks in equilibrium-which are likely to yield more accurate results than other functions used in previous studies. The images used for the fits come from the Spitzer Survey of Stellar Structure in Galaxies (S(4)G). We found that thick disks are on average more massive than previously reported, mostly due to the selected fitting function. Typically, the thin and thick disks have similar masses. We also found that thick disks do not flare significantly within the observed range in galactocentric radii and that the ratio of thick-to-thin disk scale heights is higher for galaxies of earlier types. Our results tend to favor an in situ origin for most of the stars in the thick disk. In addition, the thick disk may contain a significant amount of stars coming from satellites accreted after the initial buildup of the galaxy and an extra fraction of stars coming from the secular heating of the thin disk by its own overdensities. Assigning thick disk light to the thin disk component may lead to an underestimate of the overall stellar mass in galaxies because of different mass-to-light ratios in the two disk components. On the basis of our new results, we estimate that disk stellar masses are between 10% and 50% higher than previously thought and we suggest that thick disks are a reservoir of 'local missing baryons.'</P>

BREAKS IN THIN AND THICK DISKS OF EDGE-ON GALAXIES IMAGED IN THE<i>SPITZER</i>SURVEY OF STELLAR STRUCTURE IN GALAXIES (S⁴G)

Comeró,n, Sé,bastien,Elmegreen, Bruce G.,Salo, Heikki,Laurikainen, Eija,Athanassoula, E.,Bosma, Albert,Knapen, Johan H.,Gadotti, Dimitri A.,Sheth, Kartik,Hinz, Joannah L.,Regan, Michael W. IOP Publishing 2012 The Astrophysical journal Vol.759 No.2

<P>Breaks in the radial luminosity profiles of galaxies have until now been mostly studied averaged over disks. Here, we study separately breaks in thin and thick disks in 70 edge-on galaxies using imaging from the Spitzer Survey of Stellar Structure in Galaxies. We built luminosity profiles of the thin and thick disks parallel to midplanes and we found that thin disks often truncate (77%). Thick disks truncate less often (31%), but when they do, their break radius is comparable with that in the thin disk. This suggests either two different truncation mechanisms-one of dynamical origin affecting both disks simultaneously and another one only affecting the thin disk-or a single mechanism that creates a truncation in one disk or in both depending on some galaxy property. Thin disks apparently antitruncate in around 40% of galaxies. However, in many cases, these antitruncations are an artifact caused by the superposition of a thin disk and a thick disk, with the latter having a longer scale length. We estimate the real thin disk antitruncation fraction to be less than 15%. We found that the ratio of the thick and thin stellar disk mass is roughly constant (0.2 < M-T/M-t < 0.7) for circular velocities v(c) > 120 km s(-1), but becomes much larger at smaller velocities. We hypothesize that this is due to a combination of a high efficiency of supernova feedback and a slower dynamical evolution in lower-mass galaxies causing stellar thin disks to be younger and less massive than in higher-mass galaxies.</P>

THE UNUSUAL VERTICAL MASS DISTRIBUTION OF NGC 4013 SEEN THROUGH THE <i>SPITZER</i> SURVEY OF STELLAR STRUCTURE IN GALAXIES (S ⁴ G)

Comeró,n, Sé,bastien,Elmegreen, Bruce G.,Knapen, Johan H.,Sheth, Kartik,Hinz, Joannah L.,Regan, Michael W.,Gil de Paz, Armando,Muñ,oz-Mateos, Juan-Carlos,Mené,ndez-Delmestre, K IOP Publishing 2011 ASTROPHYSICAL JOURNAL LETTERS - Vol.738 No.2

<P>NGC 4013 is a nearby Sb edge-on galaxy known for its 'prodigious' Hi warp and its 'giant' tidal stream. Previous work on this unusual object shows that it cannot be fitted satisfactorily by a canonical thin+thick disk structure. We have produced a new decomposition of NGC 4013, considering three stellar flattened components (thin+thick disk plus an extra and more extended component) and one gaseous disk. All four components are considered to be gravitationally coupled and isothermal. To do so, we have used the 3.6 mu m images from the Spitzer Survey of Stellar Structure in Galaxies. We find evidence for NGC 4013 indeed having a thin and a thick disk and an extra flattened component. This smooth and extended component (scale height z(EC) similar to 3 kpc) could be interpreted as a thick disk or as a squashed ellipsoidal halo and contains similar to 20% of the total mass of all three stellar components. We argue it is unlikely to be related to the ongoing merger or due to the off-plane stars from a warp in the other two disk components. Instead, we favor a scenario in which the thick disk and the extended component were formed in a two-stage process, in which an initially thick disk has been dynamically heated by a merger soon enough in the galaxy history to have a new thick disk formed within it.</P>

WIGGLE INSTABILITY OF GALACTIC SPIRAL SHOCKS: EFFECTS OF MAGNETIC FIELDS

Kim, Yonghwi,Kim, Woong-Tae,Elmegreen, Bruce G. IOP Publishing 2015 The Astrophysical journal Vol.809 No.1

<P>It has been suggested that the wiggle instability (WI) of spiral shocks in a galactic disk is responsible for the formation of gaseous feathers observed in grand-design spiral galaxies. We perform both a linear stability analysis and numerical simulations to investigate the effect of magnetic fields on the WI. The disk is assumed to be infinitesimally thin, isothermal, and non-self-gravitating. We control the strengths of magnetic fields and spiral-arm forcing using the dimensionless parameters beta and F, respectively. By solving the perturbation equations as a boundary-eigenvalue problem, we obtain dispersion relations of the WI for various values of beta = 1-infinity and F = 5% and 10%. We find that the WI arising from the accumulation of potential vorticity at disturbed shocks is suppressed, albeit not completely, by magnetic fields. The stabilizing effect of magnetic fields is not from the perturbed fields but from the unperturbed fields that reduce the density compression factor in the background shocks. When F= 5% and beta less than or similar to 10 or F = 10% and beta similar to 5-10, the most unstable mode has a wavelength of similar to 0.1-0.2 times the arm-to-arm separation, which appears consistent with a mean spacing of observed feathers.</P>

Investigating HI superclouds, molecular clouds, and star formation in the outer Carina spiral arm

Geumsook Park,Bon-Chul Koo,Kee-Tae Kim,Bruce Elmegreen 한국천문학회 2023 天文學會報 Vol.48 No.2

A Study of Two Dwarf Irregular Galaxies with Asymmetrical Star Formation Distributions

Hunter, Deidre A.,Gallardo, Samavarti,Zhang, Hong-Xin,Adamo, Angela,Cook, David O.,Oh, Se-Heon,Elmegreen, Bruce G.,Kim, Hwihyun,Kahre, Lauren,Ubeda, Leonardo,Bright, Stacey N.,Ryon, Jenna E.,Fumagalli American Astronomical Society 2018 The Astrophysical journal Vol.855 No.1

<P>Two dwarf irregular galaxies, DDO 187 and NGC 3738, exhibit a striking pattern of star formation: intense star formation is taking place in a large region occupying roughly half of the inner part of the optical galaxy. We use data on the H I distribution and kinematics and stellar images and colors to examine the properties of the environment in the high star formation rate (HSF) halves of the galaxies in comparison with the low star formation rate halves. We find that the pressure and gas density are higher on the HSF sides by 30%-70%. In addition we find in both galaxies that the H I velocity fields exhibit significant deviations from ordered rotation and there are large regions of high-velocity dispersion and multiple velocity components in the gas beyond the inner regions of the galaxies. The conditions in the HSF regions are likely the result of large-scale external processes affecting the internal environment of the galaxies and enabling the current star formation there.</P>

UNVEILING THE STRUCTURE OF BARRED GALAXIES AT 3.6 μm WITH THE SPITZER SURVEY OF STELLAR STRUCTURE IN GALAXIES (S⁴G). I. DISK BREAKS

Kim, Taehyun,Gadotti, Dimitri A.,Sheth, Kartik,Athanassoula, E.,Bosma, Albert,Lee, Myung Gyoon,Madore, Barry F.,Elmegreen, Bruce,Knapen, Johan H.,Zaritsky, Dennis,Ho, Luis C.,Comeró,n, Sé IOP Publishing 2014 The Astrophysical journal Vol.782 No.2

<P>We have performed two-dimensional multicomponent decomposition of 144 local barred spiral galaxies using 3.6 mu m images from the Spitzer Survey of Stellar Structure in Galaxies. Our model fit includes up to four components (bulge, disk, bar, and a point source) and, most importantly, takes into account disk breaks. We find that ignoring the disk break and using a single disk scale length in the model fit for Type II (down-bending) disk galaxies can lead to differences of 40% in the disk scale length, 10% in bulge-to-total luminosity ratio (B/T), and 25% in bar-to-total luminosity ratios. We find that for galaxies with B/T >= 0.1, the break radius to bar radius, r(br)/R-bar, varies between 1 and 3, but as a function of B/T the ratio remains roughly constant. This suggests that in bulge-dominated galaxies the disk break is likely related to the outer Lindblad resonance of the bar and thus moves outward as the bar grows. For galaxies with small bulges, B/T < 0.1, r(br)/R-bar spans a wide range from 1 to 6. This suggests that the mechanism that produces the break in these galaxies may be different from that in galaxies with more massive bulges. Consistent with previous studies, we conclude that disk breaks in galaxies with small bulges may originate from bar resonances that may be also coupled with the spiral arms, or be related to star formation thresholds.</P>