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We use the measured B-band axial ratios of galaxies from an updated catalogue of Local Volume galaxies to determine the intrinsic shape of dwarf
irregular galaxies (de Vaucouleurs’ morphological types 8–10). We find that the shapes change systematically with luminosity,
with fainter galaxies being thicker. In particular, we divide our sample into s...
Contexts in source publication
Context 1
... best fit simulated distributions to the observed distributions for each of the sub-samples are shown in Figure 4. The intrinsic distri- butions corresponding to these apparent distributions are given in Table 2, and are shown in Figure 5. For estimating the error on the parameters, for each of the three sub-samples we define the confi- dence interval as the parameter space around the best fit parameters which give rise to simulated distributions that match the observed binned distribution at each point within Poisson errors due to bin- ning. ...
Context 2
... estimating the error on the parameters, for each of the three sub-samples we define the confi- dence interval as the parameter space around the best fit parameters which give rise to simulated distributions that match the observed binned distribution at each point within Poisson errors due to bin- ning. The extent of each parameter within confidence intervals thus defined for each of the three sub-samples are given in Table 2. The confidence intervals for p0 and q0, the two parameters of interest are also shown in Figure 6. ...
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Citations
... Stellar kinematics was crucial for establishing that, among the local giant elliptical population, it is only the the most massive ellipticals that are truly round or mildly triaxial whereas lowermass ellipticals are more akin to lenticular galaxies (Binney 1985;Franx et al. 1991;Ryden 1992;Tremblay & Merritt 1995;Kormendy & Bender 1996;Emsellem et al. 2007Emsellem et al. , 2011Cappellari 2016;Ene et al. 2018;Li et al. 2018). Nearby dwarfs also generally appear to be a combination of oblate and spheroidal 3D ellipsoids (Caldwell 1983;Ichikawa et al. 1986;Ferguson & Sandage 1989;Ichikawa 1989;Staveley-Smith et al. 1992;Ferguson & Binggeli 1994;Ryden & Terndrup 1994;Binggeli & Popescu 1995;Sung et al. 1998;Sánchez-Janssen et al. 2010;Roychowdhury et al. 2013;van der Wel et al. 2014a;Burkert 2017;Putko et al. 2019;Kado-Fong et al. 2020Rong et al. 2020). ...
The 3D geometries of high-redshift galaxies remain poorly understood. We build a differentiable Bayesian model and use Hamiltonian Monte Carlo to efficiently and robustly infer the 3D shapes of star-forming galaxies in James Webb Space Telescope Cosmic Evolution Early Release Science observations with log M * / M ⊙ = 9.0 – 10.5 at z = 0.5–8.0. We reproduce previous results from the Hubble Space Telescope Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey in a fraction of the computing time and constrain the mean ellipticity, triaxiality, size, and covariances with samples as small as ∼50 galaxies. We find high 3D ellipticities for all mass–redshift bins, suggesting oblate (disky) or prolate (elongated) geometries. We break that degeneracy by constraining the mean triaxiality to be ∼1 for log M * / M ⊙ = 9.0 – 9.5 dwarfs at z > 1 (favoring the prolate scenario), with significantly lower triaxialities for higher masses and lower redshifts indicating the emergence of disks. The prolate population traces out a “banana” in the projected b / a – log a diagram with an excess of low- b / a , large- log a galaxies. The dwarf prolate fraction rises from ∼25% at z = 0.5–1.0 to ∼50%–80% at z = 3–8. Our results imply a second kind of disk settling from oval (triaxial) to more circular (axisymmetric) shapes with time. We simultaneously constrain the 3D size–mass relation and its dependence on 3D geometry. High-probability prolate and oblate candidates show remarkably similar Sérsic indices ( n ∼ 1), nonparametric morphological properties, and specific star formation rates. Both tend to be visually classified as disks or irregular, but edge-on oblate candidates show more dust attenuation. We discuss selection effects, follow-up prospects, and theoretical implications.
... In general, the smallest simulated galaxies tend to be rounded, although not perfectly spherical, with the DM component closer to sphericity (e.g., Bullock 2002;Orkney et al. 2023). On the other hand, the observed dwarf isolated galaxies are triaxial, but with three axes of similar lengths (e.g., Roychowdhury et al. 2013;Sánchez-Janssen et al. 2016;Putko et al. 2019). In addition to whether or not real ultralow-mass galaxies are well fitted by spherically symmetric models, independent theoretical arguments point out that this assumption is not so critical since the incompatibilities may still hold when dropped. ...
According to the current concordance cosmological model, dark matter (DM) particles are collisionless and produce self-gravitating structures with a central cusp, which, generally, is not observed. The observed density tends to a central plateau or core, explained within the cosmological model through the gravitational feedback of baryons on DM. This mechanism becomes inefficient when decreasing the galaxy’s stellar mass so that in the low-mass regime ( M ⋆ ≪ 10 ⁶ M ⊙ ) the energy provided by the baryons is insufficient to modify cusps into cores. Thus, if cores exist in these galaxies they have to reflect departures from the collisionless nature of DM. Measuring the DM mass distribution in these faint galaxies is extremely challenging; however, their stellar mass distribution can be characterized through deep photometry. Here we provide a way of using only the stellar mass distribution to constrain the underlying DM distribution. The so-called Eddington inversion method allows us to discard pairs of stellar distributions and DM potentials requiring (unphysical) negative distribution functions in the phase space. In particular, cored stellar density profiles are incompatible with the Navarro–Frenk–White (NFW) potential expected from collisionless DM if the velocity distribution is isotropic and the system spherically symmetric. Through a case-by-case analysis, we are able to relax these assumptions to consider anisotropic velocity distributions and systems that do not have exact cores. In general, stellar distributions with radially biased orbits are difficult to reconcile with NFW-like potentials, and cores in the baryon distribution tend to require cores in the DM distribution.
... In general, the smallest simulated galaxies tend to be rounded, although not perfectly spherical, with the DM component closer to sphericity (e.g., Bullock 2002;Orkney et al. 2023). On the other hand, the observed dwarf isolated galaxies are triaxial, but with three axes of similar lengths (e.g, Roychowdhury et al. 2013;Sánchez-Janssen et al. 2016;Putko et al. 2019). In addition to whether real ultra-low mass galaxies are or not well fitted by spherically symmetric models, independent theoretical arguments point out that this assumption is not so critical since the incompatibilities may still hold when dropped. ...
According to the current concordance cosmological model, the dark matter (DM) particles are collision-less and produce self-gravitating structures with a central cusp which, generally, is not observed. The observed density tends to a central plateau or core, explained within the cosmological model through the gravitational feedback of baryons on DM. This mechanism becomes inefficient when decreasing the galaxy stellar mass so that in the low-mass regime (Mstar << 10**6 Msun) the energy provided by the baryons is insufficient to modify cusps into cores. Thus, if cores exist in these galaxies they have to reflect departures from the collision-less nature of DM. Measuring the DM mass distribution in these faint galaxies is extremely challenging, however, their stellar mass distribution can be characterized through deep photometry. Here we provide a way of using only the stellar mass distribution to constrain the underlying DM distribution. The so-called Eddington inversion method allows us to discard pairs of stellar distributions and DM potentials requiring (unphysical) negative distribution functions in the phase space. In particular, cored stellar density profiles are incompatible with the Navarro, Frenk, and White (NFW) potential expected from collision-less DM if the velocity distribution is isotropic and the system spherically symmetric. Through a case-by-case analysis, we are able to relax these assumptions to consider anisotropic velocity distributions and systems which do not have exact cores. In general, stellar distributions with radially biased orbits are difficult to reconcile with NFW-like potentials, and cores in the baryon distribution tend to require cores in the DM distribution.
... Dwarfs have low rotation speeds, well below Vrot = 100 km s-1, due to their modest masses, which suggests that random dynamical events can have a major impact on the detailed velocity field. Late-type dwarf irregulars typically exhibit rotation, albeit occasionally at extremely low rates (Vrot/ 1;: velocity dispersion [45]). ...
The fact that dwarf galaxies exhibit such a wide range of behaviour, from inconspicuous low surface brightness objects to the high surface brightness blue compact objects, is one of their most striking characteristics. Compared to typical spirals, their attributes have a much wider distribution. Small systems can readily undergo a fluctuation strong enough to entirely cease the propagation of star formation, according to the stochastic self-propagating star formation model (SSPSF). The likelihood of seeing a strong enough fluctuation to stop star formation will rise as the system's size decreases since the fluctuations encountered will vary inversely with system size.Small, low-mass galaxies known as dwarfs have a major impact on how we comprehend galaxy creation and development.
... Furthermore, M33 is more complex than expected for lowluminosity galaxies, which are thought to be dominated by a single component, although the highest-mass dwarfs can have a thick disk in addition to a stellar halo (Roychowdhury et al. 2013;van der Wel et al. 2014;Kado-Fong et al. 2020Patra Nath 2020). However, M33 is proving to be more complex, with a newly confirmed centrally concentrated halo (Gilbert et al. 2022) and bar (Williams et al. 2021;A. ...
Triangulum (M33) is a low-mass, relatively undisturbed spiral galaxy that offers a new regime in which to test models of dynamical heating. In spite of its proximity, M33's dynamical heating history has not yet been well-constrained. In this work, we present the TREX Survey, the largest stellar spectroscopic survey across the disk of M33. We present the stellar disk kinematics as a function of age to study the past and ongoing dynamical heating of M33. We measure line-of-sight velocities for ∼4500 disk stars. Using a subset, we divide the stars into broad age bins using Hubble Space Telescope and Canada–France–Hawaii Telescope photometric catalogs: massive main-sequence stars and helium-burning stars (∼80 Myr), intermediate-mass asymptotic branch stars (∼1 Gyr), and low-mass red giant branch stars (∼4 Gyr). We compare the stellar disk dynamics to that of the gas using existing H i , CO, and H α kinematics. We find that the disk of M33 has relatively low-velocity dispersion (∼16 km s ⁻¹ ), and unlike in the Milky Way and Andromeda galaxies, there is no strong trend in velocity dispersion as a function of stellar age. The youngest disk stars are as dynamically hot as the oldest disk stars and are dynamically hotter than predicted by most M33-like low-mass simulated analogs in Illustris. The velocity dispersion of the young stars is highly structured, with the large velocity dispersion fairly localized. The cause of this high-velocity dispersion is not evident from the observations and simulated analogs presented here.
... Furthermore, M33 is more complex then expected for a low luminosity galaxy, which are thought to be dominated by a single component, although the highest mass dwarfs can have a thick disk in addition to a stellar halo (Roychowdhury et al. 2013;van der Wel et al. 2014;Patra Nath 2020;Kado-Fong et al. 2020. However, M33, is proving to be more complex, with a newly confirmed centrally-concentrated halo (Gilbert et al. in press) and bar (Williams et al. 2021;Smercina & et al. in preparation;Lazzarini & et al. in preparation) and the mysterious warps described above (Braun & Thilker 2004;Putman et al. 2009;Semczuk et al. 2018). ...
Triangulum, M33, is a low mass, relatively undisturbed spiral galaxy that offers a new regime in which to test models of dynamical heating. In spite of its proximity, the dynamical heating history of M33 has not yet been well constrained. In this work, we present the TREX Survey, the largest stellar spectroscopic survey across the disk of M33. We present the stellar disk kinematics as a function of age to study the past and ongoing dynamical heating of M33. We measure line of sight velocities for ~4,500 disk stars. Using a subset, we divide the stars into broad age bins using Hubble Space Telescope and Canada-France-Hawaii-Telescope photometric catalogs: massive main sequence stars and helium burning stars (~80 Myr), intermediate mass asymptotic branch stars (~1 Gyr), and low mass red giant branch stars (~4 Gyr). We compare the stellar disk dynamics to that of the gas using existing HI, CO, and Halpha kinematics. We find that the disk of M33 has relatively low velocity dispersion (~16 km/s), and unlike in the Milky Way and Andromeda galaxies, there is no strong trend in velocity dispersion as a function of stellar age. The youngest disk stars are as dynamically hot as the oldest disk stars and are dynamically hotter than predicted by most M33 like low mass simulated analogs in Illustris. The velocity dispersion of the young stars is highly structured, with the large velocity dispersion fairly localized. The cause of this high velocity dispersion is not evident from the observations and simulated analogs presented here.
... However, the distribution of the bluest ( − ) 0 ≤ 0.6 EGIPS galaxies unexpectedly changes the behaviour and falls steeper. This behavior is expected for dwarf galaxies, which are systematically thicker (Roychowdhury et al. 2013), but our sample contains too few dwarf galaxies to trace this effect robustly. ...
We present a catalogue of 16551 edge-on galaxies created using the public DR2 data of the Pan-STARRS survey. The catalogue covers the three quarters of the sky above Dec.=-30 degrees. The galaxies were selected using a convolutional neural network, trained on a sample of edge-on galaxies identified earlier in the SDSS survey. This approach allows us to dramatically improve the quality of the candidate selection and perform a thorough visual inspection in a reasonable amount of time. The catalogue provides homogeneous information on astrometry, SExtractor photometry, and non-parametric morphological statistics of the galaxies. The photometry is reliably for objects in the 13.8-17.4 r-band magnitude range. According to the HyperLeda database, redshifts are known for about 63 percent of the galaxies in the catalogue. Our sample is well separated into the red sequence and blue cloud galaxy populations. The edge-on galaxies of the red sequence are systematically Delta(g-i)~0.1 mag redder than galaxies oriented at an arbitrary angle to the observer. We found a variation of the galaxy thickness with the galaxy colour. The red sequence galaxies are thicker than the galaxies of the blue cloud. In the blue cloud, on average, thinner galaxies turn out to be bluer. In the future, based on this catalogue it is intended to explore the three-dimensional structure of galaxies of different morphologies, as well as to study the scaling relations for discs and bulges.
... Because of their small masses, rotation speeds in dwarfs are low, far below v rot = 100 km s −1 , which implies that random dynamical events can play a significant role in shaping the detailed velocity field. Late-type dwarf irregulars tend to show rotation, even though sometimes with very low rates (v rot /σ < 1; σ: velocity dispersion; e.g., [27])). On the other hand, it is hard to find rotating dwarf spheroidals. ...
Dwarf galaxies are by far the most numerous galaxies in the Universe, showing properties that are quite different from those of their larger and more luminous cousins. This review focuses on the physical and chemical properties of the interstellar medium of those dwarfs that are known to host significant amounts of gas and dust. The neutral and ionized gas components and the impact of the dust will be discussed, as well as first indications for the existence of active nuclei in these sources. Cosmological implications are also addressed, considering the primordial helium abundance and the similarity of local Green Pea galaxies with young, sometimes protogalactic sources in the early Universe.
... Structurally, this process will change the dwarf from a fairly thin disk to a mildly oblate spheroid. However, recent work has shown that low-mass isolated dIrrs are actually generally quite thick, not flattened (Kaufmann et al. 2007;Sánchez-Janssen et al. 2010;Roychowdhury et al. 2010Roychowdhury et al. , 2013. Either way, once the dSph forms, it will continue to evolve in the tidal field of the host via both tidal stripping and tidal heating (Jiang et al. 2021;Peñarrubia et al. 2008;Errani et al. 2015Errani et al. , 2018. ...
... We assume that the dwarfs are represented by a family of possibly triaxial ellipsoids, described by the three axis lengths: C < B < A. The intrinsic shapes are then given by the ratios of short to long axes and intermediate to long axes, C/A and B/A. This approach has been taken numerous times in the literature for a wide variety of galaxy samples (e.g., Lisker et al. 2007;Padilla & Strauss 2008;Roychowdhury et al. 2013;Sánchez-Janssen et al. 2010, 2016Salomon et al. 2015;Sanders & Evans 2017;Kado-Fong et al. 2020b). Most relevant to the current work, these earlier works find that early-type dwarfs (both in clusters and in the LG) are well represented by roughly oblate spheroids with intrinsic axis ratios C/A ∼ 0.5 − 0.6. ...
... Still, we compare how the LV satellite samples compare with the different subsamples considered by Sánchez-Janssen et al. (2019b) in Figure 11, comparing both C/A and B/A. Also plotted are the results from Kado-Fong et al. (2020b) for higher-mass dwarfs 24 and the results from analyzing dIrrs from the UNGC of Roychowdhury et al. (2013). Additionally, we include an analysis of our "field-isolated" late-type sample. ...
The structure of a dwarf galaxy is an important probe of the effects of stellar feedback and environment. Using an unprecedented sample of 223 low-mass satellites from the ongoing Exploration of Local Volume Satellites survey, we explore the structures of dwarf satellites in the mass range 10 5.5 < M ⋆ < 10 8.5 M ⊙ . We survey satellites around 80% of the massive, M K < − 22.4 mag, hosts in the Local Volume (LV). Our sample of dwarf satellites is complete to luminosities of M V <−9 mag and surface brightness μ 0, V < 26.5 mag arcsec ⁻² within at least ∼200 projected kpc of the hosts. For this sample, we find a median satellite luminosity of M V = −12.4 mag, median size of r e = 560 pc, median ellipticity of ϵ = 0.30, and median Sérsic index of n = 0.72. We separate the satellites into late- and early-type (29.6% and 70.4%, respectively). The mass–size relations are very similar between them within ∼5%, which indicates that the quenching and transformation of a late-type dwarf into an early-type one involves only very mild size evolution. Considering the distribution of apparent ellipticities, we infer the intrinsic shapes of the early- and late-type samples. Combining with literature samples, we find that both types of dwarfs are described roughly as oblate spheroids that get more spherical at fainter luminosities, but early-types are always rounder at fixed luminosity. Finally, we compare the LV satellites with dwarf samples from the cores of the Virgo and Fornax clusters. We find that the cluster satellites show similar scaling relations to the LV early-type dwarfs but are roughly 10% larger at fixed mass, which we interpret as being due to tidal heating in the cluster environments. The dwarf structure results presented here are a useful reference for simulations of dwarf galaxy formation and the transformation of dwarf irregulars into spheroidals.
... It has long been observed that dwarf galaxies host extended, round old stellar populations reminiscent in structure to the stellar halos of massive galaxies (Lin & Faber 1983;Minniti & Zijlstra 1996;Minniti et al. 1999;Zaritsky et al. 2000;Hidalgo et al. 2003;Demers et al. 2006;Bernard et al. 2007;Stinson et al. 2009;Strader et al. 2012;Nidever et al. 2019a,b;Pucha et al. 2019;Kado-Fong et al. 2020). Recently, it has been shown that high-mass dwarfs (10 8.5 < M < 10 9.6 M ) can form a thick stellar & HI disk (Roychowdhury et al. 2013;van der Wel et al. 2014;Nath Patra 2020) in conjunction with a round stellar halo (Kado-Fong et al. 2020). ...
Extended, old, and round stellar halos appear to be ubiquitous around high-mass dwarf galaxies ($10^{8.5}<M_\star/M_\odot<10^{9.6}$) in the observed universe. However, it is unlikely that these dwarfs have undergone a sufficient number of minor mergers to form stellar halos that are composed of predominantly accreted stars. Here, we demonstrate that FIRE-2 (Feedback in Realistic Environments) cosmological zoom-in simulations are capable of producing dwarf galaxies with realistic structure, including both a thick disk and round stellar halo. Crucially, these stellar halos are formed in-situ, largely via the outward migration of disk stars. However, there also exists a large population of "non-disky" dwarfs in FIRE that lack a well-defined disk/halo and do not resemble the observed dwarf population. These non-disky dwarfs tend to be either more gas poor or to have burstier recent star formation histories than the disky dwarfs, suggesting that star formation feedback may be preventing disk formation. Both classes of dwarfs underscore the power of a galaxy's intrinsic shape -- which is a direct quantification of the distribution of the galaxy's stellar content -- to interrogate the feedback implementation in simulated galaxies.
