Low-mass Spiral Galaxies Research Articles

Quantifying the stellar ages of dynamically separated bulges and disks of CALIFA spiral galaxies

We employ a recently developed population-orbit superposition technique to simultaneously fit the stellar kinematic and age maps of 82 CALIFA spiral galaxies and obtain the ages of stars in different dynamical structures. We first evaluated the capabilities of this method on CALIFA-like mock data created from the Auriga simulations. The recovered mean ages of dynamically cold, warm, and hot components match the true values well, with an observational error of up to 20% in the mock age maps. For CALIFA spiral galaxies, we find that the stellar ages of the cold, warm, and hot components all increase with the stellar mass of the galaxies, from tcold ~ 2.2 Gyr, twarm ~ 2.3 Gyr, and thot ~ 2.6 Gyr for galaxies with stellar mass M* < 1010 M⊙, to tcold ~ 4.0 Gyr, twarm ~ 5.1 Gyr, and thot ~ 5.9 Gyr for galaxies with M* > 1011 M⊙. About 80% of the galaxies in our sample have thot > tcold, and the mean values of thot − tcold also increase with stellar mass, from 0.7−0.2+0.6 Gyr in low-mass galaxies (108.9 M⊙ < M* ≤ 1010.5 M⊙) to 1.7−0.2+0.7 Gyr in high-mass galaxies (1010.5 M⊙ < M* < 1011.3 M⊙). The stellar age is younger in disks than in bulges, on average. This suggests that either the disks formed later and/or that they experienced a more prolonged and extensive period of star formation. Lower-mass spiral galaxies have younger bulges and younger disks, while higher-mass spiral galaxies generally have older bulges, and their disks span a wide range of ages. This is consistent with the scenario in which the bulges in more massive spirals formed earlier than those in less massive spirals.

The distribution of dust in edge-on galaxies: I. The global structure

ABSTRACT In this first paper in a series we present a study of the global dust emission distribution in nearby edge-on spiral galaxies. Our sample consists of 16 angularly large and 13 less spatially resolved galaxies selected from the DustPedia sample. To explore the dust emission distribution, we exploit the Herschel photometry in the range 100–500 $\mu $m. We employ Sérsic and 3D disc models to fit the observed 2D profiles of the galaxies. Both approaches give similar results. Our analysis unequivocally states the case for the presence of extraplanar dust in between 6 and 10 large galaxies. The results reveal that both the disc scale length and height increase as a function of wavelength between 100 and 500 $\mu $m. The dust disc scale height positively correlates with the dust disc scale length, similar to what is observed for the stellar discs. We also find correlations between the scale lengths and scale heights in the near- and far-infrared which suggest that the stellar discs and their dust counterparts are tightly connected. Furthermore, the intrinsic flattening of the dust disc is inversely proportional to the maximum rotation velocity and the dust mass of the galaxy: more massive spiral galaxies host, on average, relatively thinner dust discs. Also, there is a tendency for the dust-to-stellar scale height ratio to decrease with the dust mass and rotation velocity. We conclude that low-mass spiral galaxies host a diffuse, puffed-up dust disc with a thickness similar to that of the stellar disc.

Inside-out star formation quenching and the need for a revision of bulge-disk decomposition concepts for spiral galaxies

Our knowledge about the photometric and structural properties of bulges in late-type galaxies (LTGs) is founded upon image decomposition into a Sérsic model for the central luminosity excess of the bulge and an exponential model for the more extended underlying disk. We argue that the standard practice of adopting an exponential model for the disk all the way to its center is inadequate because it implicitly neglects the fact of star formation (SF) quenching in the centers of LTGs. Extrapolating the fit to the observable star-forming zone of the disk (outside the bulge) inwardly overestimates the true surface brightness of the disk in its SF-quenched central zone (beneath the bulge). We refer to this effect as δio. Using predictions from evolutionary synthesis models and by applying to integral field spectroscopy data REMOVEYOUNG, a tool that allows the suppression of stellar populations younger than an adjustable age cutoff we estimate the δio in the centers of massive SF-quenched LTGs to be up to ∼2.5 (0.7) B (K) mag. The primary consequence of the neglect of δio in bulge-disk decomposition studies is the oversubtraction of the disk underneath the bulge, leading to a systematic underestimation of the true luminosity of the latter. Secondary biases impact the structural characterization (e.g., Sérsic exponent η and effective radius) and color gradients of bulges, and might include the erroneous classification of LTGs with a moderately faint bulge as bulgeless disks. Framed in the picture of galaxy downsizing and inside-out SF quenching, δio is expected to differentially impact galaxies across redshift and stellar mass ℳ⋆, thus leading to systematic and complex biases in the scatter and slope of various galaxy scaling relations. We conjecture that correction for the δio effect will lead to a down-bending of the bulge versus supermassive black hole relation for galaxies below log(ℳ⋆/M⊙) ∼ 10.7. A decreasing ℳ∙/ℳ⋆ ratio with decreasing ℳ⋆ would help to consistently explain the scarcity and weakness of accretion-powered nuclear activity in low-mass spiral galaxies. Finally, it is pointed out that a well-detectable δio (> 2 r mag) can emerge early on through inward migration of star-forming clumps from the disk in combination with a strong contrast of emission-line equivalent widths between the quenched protobulge and its star-forming periphery. Spatially resolved studies of δio with the James Webb Space Telescope, the Extremely Large Telescope, and Euclid could therefore offer key insights into the chronology and physical drivers of SF-quenching in the early phase of galaxy assembly.

The Brightest Stars of Irregular and Low-Mass Spiral Galaxies

A search for a correlation between the luminosities of the brightest stars and luminosities of their host galaxies was carried out on archived Hubble Space Telescope (HST) F606W or F555W (V) and F814W (I) images of about 150 nearby galaxies. The sample contains only galaxies with on-going star formation (SF) and with known distances we derived with the TRGB-method. We correlated the average absolute luminosities of the three brightest blue and the three brightest red stars with the luminosity of a host. We found a linear relation for both the blue and the red stars in irregular and low-mass spiral galaxies. Their scatters are sufficiently small (0.m4) to make this relations useful for distance determination for low-mass galaxies. We found that all 31 dwarf galaxies (M_B>-13m) in our sample lack bright stars (M_V(BS)< -7.m0), probably due to the physical conditions that prevent their birth. For galaxies with higher luminosity in the range -18m<M_B<-13m, there is an asymmetry in the distribution of the number of galaxies relative to the linear dependence, indicating an increase in the fraction of galaxies with bright stars.

Abundance of dwarf galaxies around low-mass spiral galaxies in the Local Volume

The abundance of satellite dwarf galaxies has long been considered a crucial test for the current model of cosmology leading to the well-known missing satellite problem. Recent advances in simulations and observations have allowed the study of dwarf galaxies around host galaxies in more detail. Using the Dark Energy Camera we surveyed a 72 deg2 area of the nearby Sculptor group, also encompassing the two low-mass Local Volume galaxies NGC 24 and NGC 45 residing behind the group, to search for as yet undetected dwarf galaxies. Apart from the previously known dwarf galaxies we found only two new candidates down to a 3σ surface brightness detection limit of 27.4 r mag arcsec−2. Both systems are in projection close to NGC 24. However, one of these candidates could be an ultra-diffuse galaxy associated with a background galaxy. We compared the number of known dwarf galaxy candidates around NGC 24, NGC 45, and five other well-studied low-mass spiral galaxies (NGC 1156, NGC 2403, NGC 5023, M 33, and the LMC) with predictions from cosmological simulations, and found that for the stellar-to-halo mass models considered, the observed satellite numbers tend to be on the lower end of the expected range. This could mean either that there is an overprediction of luminous subhalos in ΛCDM or that we are missing some of the satellite members due to observational biases.

How massive can a spiral galaxy be?

Galaxies The most massive galaxies in the Universe are all giant ellipticals, formed in major merger events. Spiral galaxies form more quiescently, by accreting gas from the intergalactic medium. Ogle et al. observed a sample of the most massive spiral galaxies known. For each galaxy, they separately determined the mass of stars and the mass of the surrounding dark matter halo. At the highest masses, the sample diverges from well-known scaling laws that describe lower-mass spiral galaxies, implying a maximum spiral galaxy stellar mass of about 1011.8 solar masses. These galaxies are very efficient at converting gas into stars, which may relate to the apparent mass limit. Astrophys. J. Lett. 884 , L11 (2019).

A comparison of star formation history between NGC 300 and M33

AbstractNGC 300 is a near-optical twin of the Local Group galaxy M33, which are benchmarks for understanding late-type spiral galaxies. They are two bulgeless and low-mass spiral galaxies in different environments. In order to explore the common properties and differences between the two nearby low-mass systems, we first use the simple chemical evolution model to explore the star formation history (SFH) of NGC300 and M33, and then compare the feasible model predicted SFH of NGC 300 with that of M33. Through comparing the SFHs between them, it can be found that the mean stellar age of NGC 300 is older than that of M33, there is a recent lack of primordial gas infall onto the disk of NGC 300, recent star formation along the disk of NGC 300 is less active than that of M33, and the local environment may play a key role in the secular evolution of a galaxy.

The dichotomy of dark matter fraction and total mass density slope of galaxies over five dex in mass

AbstractWe analyse the mass density distribution in the centres of galaxies across five orders of magnitude in mass range. Using high-quality spiral galaxy rotation curves and infrared photometry from SPARC, we conduct a systematic study of their central dark matter (DM) fraction (fDM) and their mass density slope (α), within their effective radius. We show that lower mass spiral galaxies are more DM dominated and have more shallow mass density slopes when compared with more massive galaxies, which have density profiles closer to isothermal. Low-mass (${M_{*}}\lesssim 10^{10}\, {\mathrm{M}_\odot}$) gas-rich spirals span a wide range of fDM values, but systematically lower than in gas-poor systems of similar mass. With increasing galaxy mass, the values of fDM decrease and the density profiles steepen. In the most massive late-type gas-poor galaxies, a possible flattening of these trends is observed. When comparing these results to massive (${M_{*}}\gtrsim 10^{10}\, {\mathrm{M}_\odot}$) elliptical galaxies from SPIDER and to dwarf ellipticals (dEs) from SMACKED, these trends result to be inverted. Hence, the values of both fDM and α, as a function of M*, exhibit a U-shape trend. At a fixed stellar mass, the mass density profiles in dEs are steeper than in spirals. These trends can be understood by stellar feedback from a more prolonged star formation period in spirals, causing a transformation of the initial steep density cusp to a more shallow profile via differential feedback efficiency by supernovae, and by galaxy mergers or AGN feedback in higher mass galaxies.

Metallicity gradients in small and nearby spiral galaxies

ABSTRACT Spectra of H ii regions obtained with Gemini/GMOS are used to derive the radial metallicity gradients of four small, low-mass spiral galaxies. The analysis of the outer disc of one of them, NGC 1058, uncovers the characteristic flattening found in similar extended disc galaxies. After combining these data with published long-slit observations of nearby spiral galaxies, no evidence for a dependence of the disc scale length-normalized metallicity gradients with stellar mass is found, down to log (M⋆/M⊙) ∼ 8.5. The abundance gradients derived from these observations are compared to predictions from recent cosmological simulations of galaxy evolution, finding that in several cases the simulations fail to reproduce the mean steepening of the gradients, expressed in dex kpc−1, with decreasing stellar mass for present-day galaxies, or do not extend to sufficiently small stellar masses for a meaningful comparison. The mean steepening of the abundance gradients (in dex kpc−1) with decreasing disc scale length is in qualitative agreement with predictions from the inside-out model of Boissier &amp; Prantzos, although the predicted slopes are systematically steeper than observed. This indicates the necessity of including processes such as outflows and radial mixing in similar models of galactic chemical evolution. Published spatially resolved metallicity and photometric data of dwarf irregular galaxies suggest that significant, but transitory, metallicity gradients can develop for systems that have experienced recent (t &amp;lt; 100 Myr) enhanced star formation in their inner discs.

Sizes of Stellar Subsystems of Disk Galaxies and the Metallicities of Red Giants

Stellar photometry of 53 low-mass spiral and irregular galaxies has been carried out using archival frames obtained by the Hubble Space Telescope. Young and old stars (blue supergiants and red giants) are distinguished on the resulting Hertzsprung–Russell diagrams, and the spatial sizes of the subsystems formed by these stars are determined. A correlation is found between the metallicities of red giants and the difference between the linear sizes of stellar systems of different ages. This dependence can be explained if the sizes of stellar subsystems expand over the lifetimes of galaxies, as well as the influence of the relationship between the mass of a galaxy and the metallicity of its stars.

Multiple mechanisms quench passive spiral galaxies

We examine the properties of a sample of 35 nearby passive spiral galaxies in order to determine their dominant quenching mechanism(s). All five low mass ($\textrm{M}_{\star} < 1 \times 10^{10} \textrm{M}_{\odot}$) passive spiral galaxies are located in the rich Virgo cluster. This is in contrast to low mass spiral galaxies with star formation, which inhabit a range of environments. We postulate that cluster-scale gas stripping and heating mechanisms operating only in rich clusters are required to quench low mass passive spirals, and ram-pressure stripping and strangulation are obvious candidates. For higher mass passive spirals, while trends are present, the story is less clear. The passive spiral bar fraction is high: 74$\pm$15%, compared with 36$\pm$5% for a mass, redshift, and T-type matched comparison sample of star forming spiral galaxies. The high mass passive spirals occur mostly, but not exclusively, in groups, and can be central or satellite galaxies. The passive spiral group fraction of 74$\pm$15% is similar to that of the comparison sample of star forming galaxies at 61$\pm$7%. We find evidence for both quenching via internal structure and environment in our passive spiral sample, though some galaxies have evidence of neither. From this, we conclude no one mechanism is responsible for quenching star formation in passive spiral galaxies - rather, a mixture of mechanisms are required to produce the passive spiral distribution we see today.

Carbon and oxygen abundance gradients in NGC 300 and M33 from optical recombination lines

We present deep spectrophotometry of several Hii regions in the nearby low-mass spiral galaxies NGC 300 and M33. The data have been taken with UVES and OSIRIS spectrographs attached to the 8m VLT and 10.4m GTC telescopes, respectively. We have derived precise values of the physical conditions for each object making use of several emission line-intensity ratios. In particular, we have obtained direct determinations of the electron temperature in all the observed objects. We detect pure recombination lines (RLs) of Cii and Oii in several of the Hii regions, permitting to derive their C/H and C/O ratios. We have derived the radial abundance gradient of O for each galaxy making use of collisionally excited lines (CELs) and RLs, as well as the C and N gradients using RLs and CELs, respectively. We obtain the first determination of the C/H gradient of NGC 300 and improve its determination in the case of M33. In both galaxies, the C/H gradients are steeper that those of O/H, leading to negative C/O gradients. Comparing with similar results for other spiral galaxies, we find a strong correlation between the slope of the C/H gradient and M_V. We find that some Hii regions located close to the isophotal radius (R_25) of NGC 300 and M33 show C/O ratios more similar to those typical of dwarf galaxies than those of Hii regions in the discs of more massive spirals. This may be related to the absence of flattening of the gradients in the external parts of NGC 300 and M33. Finally, we find very similar N/H gradients in both galaxies and a fair correlation between the slope of the N/H gradient and M_V comparing with similar data for a sample of spiral galaxies.

Star formation rates in isolated galaxies selected from the Two-Micron All-Sky Survey

We have considered the star formation properties of 1616 isolated galaxies from the 2MASS XSC selected sample (2MIG) with the FUV GALEX magnitudes. This sample was then compared with corresponding properties of isolated galaxies from the Local Orphan Galaxies catalogue (LOG) and paired galaxies. We found that different selection algorithms define different populations of isolated galaxies. The population of the LOG catalogue, selected from non-clustered galaxies in the Local Supercluster volume, mostly consists of low-mass spiral and late type galaxies. The SSFR upper limit in isolated and paired galaxies does not exceed the value of ~dex(-9.4). This is probably common for galaxies of differing activity and environment (at least at z 11.5 have higher (S)SFR than isolated galaxies. Our results suggest that the environment helps to trigger the star formation in the highest mass galaxies. We found that the fraction of AGN in the paired sample is only a little higher than in our isolated galaxy sample. We assume that AGN phenomenon is probably defined by secular galaxy evolution.

HOT GASEOUS CORONAE AROUND SPIRAL GALAXIES: PROBING THE ILLUSTRIS SIMULATION

The presence of hot gaseous coronae around present-day massive spiral galaxies is a fundamental prediction of galaxy formation models. However, our observational knowledge remains scarce, since to date only four gaseous coronae were detected around spirals with massive stellar bodies ($\gtrsim2\times10^{11} \ \rm{M_{\odot}}$). To explore the hot coronae around lower mass spiral galaxies, we utilized Chandra X-ray observations of a sample of eight normal spiral galaxies with stellar masses of $(0.7-2.0)\times10^{11} \ \rm{M_{\odot}}$. Although statistically significant diffuse X-ray emission is not detected beyond the optical radii ($\sim20$ kpc) of the galaxies, we derive $3\sigma$ limits on the characteristics of the coronae. These limits, complemented with previous detections of NGC 1961 and NGC 6753, are used to probe the Illustris Simulation. The observed $3\sigma$ upper limits on the X-ray luminosities and gas masses exceed or are at the upper end of the model predictions. For NGC 1961 and NGC 6753 the observed gas temperatures, metal abundances, and electron density profiles broadly agree with those predicted by Illustris. These results hint that the physics modules of Illustris are broadly consistent with the observed properties of hot coronae around spiral galaxies. However, a shortcoming of Illustris is that massive black holes, mostly residing in giant ellipticals, give rise to powerful radio-mode AGN feedback, which results in under luminous coronae for ellipticals.

Angular Momentum across the Hubble sequence from the CALIFA survey

AbstractWe investigate the stellar angular momentum of galaxies across the Hubble sequence from the CALIFA survey. The distribution of CALIFA elliptical and lenticular galaxies in the λRe - εe diagram is consistent with that shown by the Atlas3D survey. Our data, however, show that the location of spiral galaxies in this diagram is significantly different. We have found two families of spiral galaxies with particularly peculiar properties: (a) spiral galaxies with much higher λRe values than any elliptical and lenticular galaxy; (b) low-mass spiral galaxies with observed λRe values much lower than expected for their apparent flattening. We use these two families of objects to argue that (1) fading alone cannot explain the transformation of spiral to lenticular galaxies, and (2) that those low-mass spiral galaxies are in fact dark matter dominated, which explains the unusually low angular momentum.

PITCH ANGLE RESTRICTIONS IN LATE-TYPE SPIRAL GALAXIES BASED ON CHAOTIC AND ORDERED ORBITAL BEHAVIOR

We built models for low bulge mass spiral galaxies (late type as defined by the Hubble classification) using a 3-D self-gravitating model for spiral arms, and analyzed the orbital dynamics as a function of pitch angle, going from 10$\deg$ to 60$\deg$. Testing undirectly orbital self-consistency, we search for the main periodic orbits and studied the density response. For pitch angles up to approximately $\sim 20\deg$, the response supports closely the potential permitting readily the presence of long lasting spiral structures. The density response tends to "avoid" larger pitch angles in the potential, by keeping smaller pitch angles in the corresponding response. Spiral arms with pitch angles larger than $\sim 20\deg$, would not be long-lasting structures but rather transient. On the other hand, from an extensive orbital study in phase space, we also find that for late type galaxies with pitch angles larger than $\sim 50\deg$, chaos becomes pervasive destroying the ordered phase space surrounding the main stable periodic and quasi-periodic orbits and even destroying them. This result is in good agreement with observations of late type galaxies, where the maximum observed pitch angle is $\sim 50\deg$.

A Large Dark Matter Core in the Fornax Dwarf Spheroidal Galaxy?

We use measurements of the stellar velocity dispersion profile of the Fornax dwarf spheroidal galaxy to derive constraints on its dark matter distribution. Though the data are unable to distinguish between models with small cores and those with cusps, we show that a large > 1 kpc dark matter core in Fornax is highly implausible. Irrespective of the origin of the core, reasonable dynamical limits on the mass of the Fornax halo constrain its core radius to be no larger than 700 pc. We derive an upper limit core radius of 300 pc by demanding that the central phase space density of Fornax not exceed that directly inferred from the rotation curves of low-mass spiral galaxies. Further, if the halo is composed of warm dark matter then phase-space constraints force the core to be quite small in order to avoid conservative limits from the Ly alpha forest power spectrum, implying a core radius < 85 pc. We discuss our results in the context of the idea that the extended globular cluster distribution in Fornax can be explained by the presence of a large 1.5 kpc core. A self-consistent core of this size would be drastically inconsistent with the expectations of standard warm or cold dark matter models, and would also require an unreasonably massive dark matter halo, with a maximum circular velocity of 200 km/s.

High‐Resolution Measurements of the Halos of Four Dark Matter–Dominated Galaxies: Deviations from a Universal Density Profile

We derive rotation curves for four nearby, low-mass spiral galaxies and use them to constrain the shapes of their dark matter density profiles. This analysis is based on high-resolution two-dimensional Hα velocity fields of NGC 4605, NGC 5949, NGC 5963, and NGC 6689 and CO velocity fields of NGC 4605 and NGC 5963. In combination with our previous study of NGC 2976, the full sample of five galaxies contains density profiles that span the range from αDM = 0 to αDM = 1.20, where αDM is the power-law index describing the central density profile. The scatter in αDM from galaxy to galaxy is 0.44, 3 times as large as in cold dark matter (CDM) simulations, and the mean density profile slope is αDM = 0.73, shallower than that predicted by the simulations. These results call into question the hypothesis that all galaxies share a universal dark matter density profile. We show that one of the galaxies in our sample, NGC 5963, has a cuspy density profile that closely resembles those seen in CDM simulations, demonstrating that while galaxies with the steep central density cusps predicted by CDM do exist, they are in the minority. In spite of these differences between observations and simulations, the relatively cuspy density profiles we find do not suggest that this problem represents a crisis for CDM. Improving the resolution of the simulations and incorporating additional physics may resolve the remaining discrepancies. We also find that four of the galaxies contain detectable radial motions in the plane of the galaxy. We investigate the hypothesis that these motions are caused by a triaxial dark matter halo and place lower limits on the ellipticity of the orbits in the plane of the disk of 0.043-0.175.

Low-mass spiral galaxies with little molecular gas and prodigious star formation

view Abstract Citations (61) References (34) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Low-Mass Spiral Galaxies with Little Molecular Gas and Prodigious Star Formation Kenney, Jeffrey D. ; Young, Judith S. Abstract A comparison of CO and H I properties of Virgo cluster galaxies reveals a population of H I-rich, CO-poor, lower mass Sbc-Sm spiral galaxies undergoing prodigious massive star formation. Some of these galaxies exhibit radial H I surface density profiles which increase continuously toward the center, and have central H I surface densities as high as 5 x 10^21^ cm^-2^, which is several times greater than the H I surface densities in more massive, H_2_-dominated spirals. This implies that the weak CO emission in these systems is due, at least in part, to a lack of H_2_. Two tracers of massive star formation, the Hα luminosity and the far-infrared luminosity, show excellent correlations with the total gas mass (H I + H_2_) within the optical diameter. Thus, within this sample of 31 Virgo Sbc-Sm galaxies, the efficiency of massive star formation does not depend strongly on whether gas is in the molecular or atomic phase. It is also concluded that a column density of 10^21^ nuclei cm^-2^ is a necessary, but insufficient condition for the creation of an H_2_-dominated interstellar medium. Some other parameter(s) related to galaxy mass influences whether gas-rich galaxies form and maintain large steady-state supplies of molecular gas. Publication: The Astrophysical Journal Pub Date: March 1988 DOI: 10.1086/166119 Bibcode: 1988ApJ...326..588K Keywords: Carbon Monoxide; H I Regions; Interstellar Gas; Spiral Galaxies; Star Formation; Virgo Galactic Cluster; Hydrogen; Molecular Gases; Astrophysics; GALAXIES: CLUSTERING; GALAXIES: INTERSTELLAR MATTER; STARS: FORMATION full text sources ADS | data products NED (31) SIMBAD (30)