Formation Of Disk Galaxies Research Articles

Understanding stellar populations in thin and thick discs of edge-on galaxies with MUSE – I. The case of the reignited S0 galaxy ESO 544-27

ABSTRACT Edge-on galaxies act as the best laboratories to understand the origin of thin and thick discs in galaxies. Measurement of spatially resolved stellar population properties in such galaxies, particularly age, metallicity, and [α/Fe], are crucial to understanding the formation and evolution of disc galaxies. Such measurements are made possible from stellar population model fits to deep integral field spectroscopic (IFU) observations of resolved galaxies. We utilize archival MUSE IFU observations of the edge-on galaxy ESO 544-27 to uncover the formation history of its thin and thick discs through its stellar populations. We find the thin disc of the galaxy is dominated by an old (>9 Gyr) low [α/Fe] metal-rich stellar population. Its outer thick disc is dominated by an old (>9 Gyr) high [α/Fe] metal-rich component that should have formed with higher star formation efficiency than the Milky Way thick disc. We thus find [α/Fe] dichotomy in ESO 544-27 with its thin and thick discs dominated by low and high [α/Fe] stellar populations, respectively. However, we also find a metal-rich younger (<2 Gyr old) stellar population in ESO 544-27. The galaxy was nearly quenched until its star formation was reignited recently first in the outer and inner thick disc (∼1 Gyr ago) and then in the thin disc (∼600 Myr ago). We thus find that both the low [α/Fe] thin and high [α/Fe] thick discs of ESO 544-27 are inhabited primarily by similarly old metal-rich stellar populations, a contrast to that of other galaxies with known thin and thick disc stellar population properties.

Clouds accreting from the IGM are not able to feed the star formation of low-redshift disc galaxies

ABSTRACT Galactic halos accrete material from the intergalactic medium (IGM) and part of this accretion is expected to be in the form of cool (T ∼ 104 K) gas. A signature of this process could reside in the detection of numerous clouds in the circumgalactic medium (CGM). However, whether this material is able to accrete onto the galaxies and feed their star formation or, instead, evaporates into the CGM hot phase (corona, T ∼ 106 K), is not yet understood. Here, we investigate the evolution of cool CGM clouds accreted from the IGM and falling through the hot corona of low-redshift disc galaxies, using 3D high-resolution hydrodynamical simulations. We include the effects of gravity due to the dark matter halo, isotropic thermal conduction, radiative cooling, and an ionizing UV background. We explored different values of parameters such as the halo mass, coronal mass, initial cloud velocity and strength of the thermal conduction. We find that the clouds lose the vast majority of their mass at distances larger than half of the galaxy virial radius and are completely dissolved in the corona before reaching the central galaxy. Resolving the Field length with at least 5–7 cells is crucial to correctly capture the evolution of the infalling cool gas. Our results indicate that cool IGM accretion can not feed star formation in z ∼ 0 star-forming galaxies in halos with masses of 1011.9 M⊙ or above. This suggests that present-day massive star-forming galaxies can sustain their star formation only via the spontaneous or induced cooling of their hot corona.

Unraveling Joint Evolution of Bars, Star Formation, and Active Galactic Nuclei of Disk Galaxies

We aim to unravel the interplay between bars, star formation (SF), and active galactic nuclei (AGNs) in barred galaxies. To this end, we utilize the SDSS DR12 to select a sample of nearby (0.02 < z < 0.06) disk galaxies that are suitable for bar examination (M r < −20.12 and inclination ≲53°). We identify 3662 barred galaxies and measure the length and axis ratio of each bar. We invent new bar parameters that mitigate the stellar and bulge mass biases and show, for the first time, that the evolution of non-AGN and AGN-hosting barred galaxies should be tracked using different bar parameters: the bar length for non-AGN galaxies and the bar axis ratio for AGN-hosting galaxies. Our analysis confirms that barred galaxies have a higher specific SF rate than unbarred control galaxies. Moreover, we find a positive correlation of bar length with both the SF enhancement and the centrally star-forming galaxy fraction, indicating the interconnectivity of bars and SF through the bar-driven gas inflow. We also find that, while the AGN fraction of barred galaxies is the same as that of the unbarred control sample, galaxies hosting more massive black holes (BHs) have rounder (i.e., higher axis ratio) bars, implying that the bar is not a cause of AGN activity; rather, AGNs appear to regulate bars. Our findings corroborate theoretical predictions that bars in non-AGN galaxies grow in length, and bars in AGN-hosting galaxies become rounder as BHs grow and eventually get destroyed.

The phase structure of cosmic ray driven outflows in stream fed disc galaxies

ABSTRACT Feeding with gas in streams is well established to be an important galaxy growth mechanism. Using an idealized set-up of an isolated galaxy, we study the impact of stream feeding (with 107 M⊙ Myr−1 rate) on the star formation and outflows of disc galaxies with ∼1011 M⊙ baryonic mass. The magnetohydrodynamical simulations are carried out with the piernik code and include star formation, feedback from supernova, and cosmic ray advection and diffusion, on a uniform grid with 195 pc spatial resolution. We find that the introduction of a cold gas stream accreted by the disc enhances galactic star formation. Lower angular momentum streams result in more compact discs, higher star formation rates and stronger outflows. In agreement with previous studies, models including cosmic rays launch stronger outflows travelling much further into the galactic halo. Cosmic ray supported outflows are also cooler than supernova only driven outflows. With cosmic rays, the star formation is suppressed and the thermal pressure is reduced. We find evidence for two distinct outflow phases. The warm outflows have high angular momentum and stay close to the galactic disc, while the hot outflow phase has low angular momentum and escapes from the centre deep into the halo. Cosmic rays can therefore have a strong impact on galaxy evolution by removing low angular momentum, possibly metal enriched gas from the disc and injecting it into the circumgalactic medium.

Morpheus Reveals Distant Disk Galaxy Morphologies with JWST: The First AI/ML Analysis of JWST Images

The dramatic first images with JWST demonstrated its power to provide unprecedented spatial detail for galaxies in the high-redshift universe. Here, we leverage the resolution and depth of the JWST Cosmic Evolution Early Release Science Survey data in the Extended Groth Strip to perform pixel-level morphological classifications of galaxies in JWST F150W imaging using the Morpheus deep-learning framework for astronomical image analysis. By cross-referencing with existing photometric redshift catalogs from the Hubble Space Telescope (HST) CANDELS survey, we show that JWST images indicate the emergence of disk morphologies before z ∼ 2 and with candidates appearing as early as z ∼ 5. By modeling the light profile of each object and accounting for the JWST point-spread function, we find the high-redshift disk candidates have exponential surface brightness profiles with an average Sérsic index 〈n〉 = 1.04 and >90% displaying “disky” profiles (n < 2). Comparing with prior Morpheus classifications in CANDELS we find that a plurality of JWST disk galaxy candidates were previously classified as compact based on the shallower HST imagery, indicating that the improved optical quality and depth of the JWST helps to reveal disk morphologies that were hiding in the noise. We discuss the implications of these early disk candidates on theories for cosmological disk galaxy formation.

The galaxy size to halo spin relation of disc galaxies in cosmological hydrodynamical simulations

ABSTRACT In the standard disc galaxy formation model, the sizes of galactic discs are tightly related to the spin parameters λ of their dark matter haloes. The model has been wildly adopted by various semi-analytical galaxy formation models which have been extremely successful to interpret a large body of observational data. However, the size–λ correlation was rarely seen in most modern hydrodynamical simulations of galaxy formation. In this short paper, we make use of 4 sets of large hydrodynamical simulations to explore the size–spin parameter relation with a large sample of simulated disc galaxies and compare it with a popular disc galaxy formation model of Mo et al. (1998). Intriguingly, galactic sizes correlate with spin parameters of their dark matter haloes in the simulations developed by the IllustrisTNG collaborations, albeit the relation does not always agree with prediction of MMW98 model overall stellar mass range we examined. There is also a size–spin correlation for the Milky Way analogies in the EAGLE simulations, while it is relatively weaker than that of the IllustrisTNG counterparts. For the dwarfs in the simulations from the EAGLE collaboration, there is NULL correlation. We conclude that either the detailed subgrid physics or hydrodynamics solvers account for the size-spin parameter relation, which will be explored in our future work.

Can ultralight dark matter explain the age–velocity dispersion relation of the Milky Way disc: A revised and improved treatment

ABSTRACT Ultralight axion-like particles ma ∼ 10−22 eV, or Fuzzy Dark Matter (FDM), behave comparably to cold dark matter (CDM) on cosmological scales and exhibit a kpc-size de Broglie wavelength capable of alleviating established (sub-)galactic-scale problems of CDM. Substructures inside an FDM halo incur gravitational potential perturbations, resulting in stellar heating sufficient to account for the Galactic disc thickening over a Hubble time, as first demonstrated by Church et al. We present a more sophisticated treatment that incorporates the full baryon and dark matter distributions of the Milky Way and adopts stellar disc kinematics inferred from recent Gaia, APOGEE, and LAMOST surveys. Ubiquitous density granulation and subhalo passages, respectively, drive inner disc thickening and flaring of the outer disc, resulting in an observationally consistent ‘U-shaped’ disc vertical velocity dispersion profile with the global minimum located near the solar radius. The observed age–velocity dispersion relation in the solar vicinity can be explained by the FDM-substructure-induced heating and places an exclusion bound ma ≳ 0.4 × 10−22 eV. We assess non-trivial uncertainties in the empirical core–halo relation, FDM subhalo mass function and tidal stripping, and stellar heating estimate. The mass range ma ≃ 0.5–0.7 × 10−22 eV favoured by the observed thick disc kinematics is in tension with several exclusion bounds inferred from dwarf density profiles, stellar streams, and Milky Way satellite populations, which could be significantly relaxed due to the aforesaid uncertainties. Additionally, strongly anisotropic heating could help explain the formation of ultra-thin disc galaxies.

The specific angular momentum of disc galaxies and its connection with galaxy morphology, bar structure, and disc gravitational instability

ABSTRACT The specific angular momenta (j ≡ J/M) of stars (j⋆), gas (jgas), baryons as a whole (jb) and dark matter haloes (jh) contain clues of vital importance about how galaxies form and evolve. Using one of the largest samples of disc galaxies (S0–BCD) with high-quality rotation curves and near-infrared surface photometry, we perform a detailed comparative analysis of j that stretches across a variety of galaxy properties. Our analysis imposes tight constraints on the ‘retained’ fractions of specific angular momentum (j⋆/jh, jH i/jh, and jb/jh), as well as on their systematic trends with mass fraction and galaxy morphology, thus on how well specific angular momentum is conserved in the process of disc galaxy formation and evolution. In particular, one of the most innovative results of our analysis is the finding that galaxies with larger baryon fractions have also retained larger fractions of their specific angular momentum. Furthermore, our analysis demonstrates how challenging it is to characterize barred galaxies from a gravitational instability point of view. This is true not only for the popular Efstathiou, Lake &amp; Negroponte bar instability criterion, which fails to separate barred from non-barred galaxies in about 55 per cent of the cases, but also for the mass-weighted Toomre parameter of atomic gas, 〈QH i〉, which succeeds in separating barred from non-barred galaxies, but only in a statistical sense.

A Theory for Galaxy Formation: Innovative Model for Evolution of Galaxies as a Function in the Initial Cloud 2π and 4π Geometry and Acceleration

The Big Bang idea is referred in the glorious Quran. As a matter of fact, there is no single integrated model describing the formation of all type of the galaxies. This work proposes a new theory and equations describing the controlling conditions and parameters of stars and galaxies formation. The derived equation called, Sayed`s galaxy formation formula (SGFF), shows that the formation of the major disk (spiral) and elliptical galaxies is correlated to the 2π and 4π geometry of the initial cloud. Sayed`s temperature (Ts) , pressure (Ps) and radius (Rs) are among the effective parameters of galaxies formation. The mass of galaxy (Sayed`s galaxy mass formula- SGME) was also deduced based on acceleration and expansion and given as a new formula. The formulas were validated and verified by check of the units and comparison with the declared values. The minimum mass (0.0774Mʘ) for star formation was calculated and found to be fully matched with the reference range; 0.075 – 0.08 solar mass, for 4π geometry. The gas halo mass of the Milky Way was calculated with ~2 % discrepancy. Our previous article; Dark matter-energy to Hydrogen-helium ratio should be considered in galaxy formation mechanism and calculation.

Observations of the initial formation and evolution of spiral galaxies at 1 &amp;lt; z &amp;lt; 3 in the CANDELS fields

ABSTRACT Many aspects concerning the formation of spiral and disc galaxies remain unresolved, despite their discovery and detailed study over the past 150 yr. As such, we present the results of an observational search for proto-spiral galaxies and their earliest formation, including the discovery of a significant population of spiral-like and clumpy galaxies at z &amp;gt; 1 in deep Hubble Space Telescope CANDELS imaging. We carry out a detailed analysis of this population, characterizing their number density evolution, masses, star formation rates (SFR), and sizes. Overall, we find a surprisingly high overall number density of massive $M_{*} \gt 10^{10}\, \mathrm{M}_{\odot }$ spiral-like galaxies (including clumpy spirals) at z &amp;gt; 1 of $0.18\, {\rm per}\, \mathrm{arcmin}^{-2}$. We measure and characterize the decline in the number of these systems at higher redshift using simulations to correct for redshift effects in identifications, finding that the true fraction of spiral-like galaxies grows at lower redshifts as ∼ (1 + z)−1.1. This is such that the absolute numbers of spirals increases by a factor of ∼10 between z = 2.5 and z = 0.5. We also demonstrate that these spiral-like systems have large sizes at z &amp;gt; 2, and high SFRs, above the main-sequence, These galaxies represent a major mode of galaxy formation in the early Universe, perhaps driven by the spiral structure itself. We finally discuss the origin of these systems, including their likely formation through gas accretion and minor mergers, but conclude that major mergers are an unlikely cause.

GASP and MaNGA Surveys Shed Light on the Enigma of the Gas Metallicity Gradients in Disk Galaxies

Abstract Making use of both MUSE observations of 85 galaxies from the survey GASP (GAs Stripping Phenomena in galaxies with MUSE) and a large sample from MaNGA (Mapping Nearby Galaxies at Apache Point Observatory survey), we investigate the distribution of gas metallicity gradients as a function of stellar mass for local cluster and field galaxies. Overall, metallicity profiles steepen with increasing stellar mass up to 1010.3 M ⊙ and flatten out at higher masses. Combining the results from the metallicity profiles and the stellar mass surface density gradients, we propose that the observed steepening is a consequence of local metal enrichment due to in situ star formation during the inside-out formation of disk galaxies. The metallicity gradient−stellar mass relation is characterized by a rather large scatter, especially for 109.8 &lt; M ⋆/M ⊙ &lt; 1010.5, and we demonstrate that metallicity gradients anti-correlate with the galaxy gas fraction. Focusing on the galaxy environment, at any given stellar mass, cluster galaxies have systematically flatter metallicity profiles than their field counterparts. Many subpopulations coexist in clusters: galaxies with shallower metallicity profiles appear to have fallen into their present host halo sooner and have experienced the environmental effects for a longer time than cluster galaxies with steeper metallicity profiles. Recent galaxy infallers, like galaxies currently undergoing ram pressure stripping, show metallicity gradients more similar to those of field galaxies, suggesting they have not felt the effect of the cluster yet.

The distribution of [α/Fe] in the Milky Way disc

ABSTRACT Using a sample of red giant stars from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) Data Release 16, we infer the conditional distribution $p([\alpha /{\rm Fe}]\, |\, [{\rm Fe}/{\rm H}])$ in the Milky Way disk for the α-elements Mg, O, Si, S, and Ca. In each bin of [Fe/H] and Galactocentric radius R, we model p([α/Fe]) as a sum of two Gaussians, representing ‘low-α’ and ‘high-α’ populations with scale heights $z_1=0.45\, {\rm kpc}$ and $z_2=0.95\, {\rm kpc}$, respectively. By accounting for age-dependent and z-dependent selection effects in APOGEE, we infer the [α/Fe] distributions that would be found for a fair sample of long-lived stars covering all z. Near the Solar circle, this distribution is bimodal at sub-solar [Fe/H], with the low-α and high-α peaks clearly separated by a minimum at intermediate [α/Fe]. In agreement with previous results, we find that the high-α population is more prominent at smaller R, lower [Fe/H], and larger |z|, and that the sequence separation is smaller for Si and Ca than for Mg, O, and S. We find significant intrinsic scatter in [α/Fe] at fixed [Fe/H] for both the low-α and high-α populations, typically ∼0.04-dex. The means, dispersions, and relative amplitudes of this two-Gaussian description, and the dependence of these parameters on R, [Fe/H], and α-element, provide a quantitative target for chemical evolution models and a test for hydrodynamic simulations of disk galaxy formation. We argue that explaining the observed bimodality will probably require one or more sharp transitions in the disk’s gas accretion, star formation, or outflow history in addition to radial mixing of stellar populations.

Formation of massive disc galaxies in the IllustrisTNG simulation

ABSTRACT We investigate the formation history of massive disc galaxies in hydrodynamical simulation – the IllustrisTNG, to study why massive disc galaxies survive through cosmic time. 83 galaxies in the simulation are selected with M*,z = 0 &amp;gt; 8 × 1010 M⊙ and kinematic bulge-to-total ratio less than 0.3. We find that 8.4 per cent of these massive disc galaxies have quiet merger histories and preserve disc morphology since formed. 54.2 per cent have a significant increase in bulge components in history, then become discs again till present time. The rest 37.3 per cent experience prominent mergers but survive to remain discy. While mergers and even major mergers do not always turn disc galaxies into ellipticals, we study the relations between various properties of mergers and the morphology of merger remnants. We find a strong dependence of remnant morphology on the orbit type of major mergers. Specifically, major mergers with a spiral-in falling orbit mostly lead to disc-dominant remnants, and major mergers of head-on galaxy–galaxy collision mostly form ellipticals. This dependence of remnant morphology on orbit type is much stronger than the dependence on cold gas fraction or orbital configuration of merger system as previously studied.

The origin of bulges and discs in the CALIFA survey – I. Morphological evolution

ABSTRACT This series of papers aims at understanding the formation and evolution of non-barred disc galaxies. We use the new spectro-photometric decomposition code, c2d, to separate the spectral information of bulges and discs of a statistically representative sample of galaxies from the CALIFA survey. Then, we study their stellar population properties analysing the structure-independent datacubes with the Pipe3D algorithm. We find a correlation between the bulge-to-total (B/T) luminosity (and mass) ratio and galaxy stellar mass. The B/T mass ratio has only a mild evolution with redshift, but the bulge-to-disc (B/D) mass ratio shows a clear increase of the disc component since redshift z &amp;lt; 1 for massive galaxies. The mass–size relation for both bulges and discs describes an upturn at high galaxy stellar masses (log (M⋆/M⊙) &amp;gt; 10.5). The relation holds for bulges but not for discs when using their individual stellar masses. We find a negligible evolution of the mass–size relation for both the most massive ($\log {(M_{\star \rm ,b,d}/{\rm M}_{\odot })} \gt 10$) bulges and discs. For lower masses, discs show a larger variation than bulges. We also find a correlation between the Sérsic index of bulges and both galaxy and bulge stellar mass, which does not hold for the disc mass. Our results support an inside-out formation of nearby non-barred galaxies, and they suggest that (i) bulges formed early-on and (ii) they have not evolved much through cosmic time. However, we find that the early properties of bulges drive the future evolution of the galaxy as a whole, and particularly the properties of the discs that eventually form around them.

Dust evolution in zoom-in cosmological simulations of galaxy formation

ABSTRACT We present cosmological zoom-in hydrodynamical simulations for the formation of disc galaxies, implementing dust evolution and dust promoted cooling of hot gas. We couple an improved version of our previous treatment of dust evolution, which adopts the two-size approximation to estimate the grain-size distribution, with the MUPPI star formation and feedback subresolution model. Our dust evolution model follows carbon and silicate dust separately. To distinguish differences induced by the chaotic behaviour of simulations from those genuinely due to different simulation set-up, we run each model six times, after introducing tiny perturbations in the initial conditions. With this method, we discuss the role of various dust-related physical processes and the effect of a few possible approximations adopted in the literature. Metal depletion and dust cooling affect the evolution of the system, causing substantial variations in its stellar, gas, and dust content. We discuss possible effects on the Spectral Energy Distribution of the significant variations of the size distribution and chemical composition of grains, as predicted by our simulations during the evolution of the galaxy. We compare dust surface density, dust-to-gas ratio, and small-to-large grain mass ratio as a function of galaxy radius and gas metallicity predicted by our fiducial run with recent observational estimates for three disc galaxies of different masses. The general agreement is good, in particular taking into account that we have not adjusted our model for this purpose.

Investigating the Formation and Evolution of Massive Disc Galaxies with the MUSE TIMER Project

Investigating the Formation and Evolution of Massive Disc Galaxies with the MUSE TIMER Project

YZiCS: Unveiling the Quenching History of Cluster Galaxies Using Phase-space Analysis

Abstract We used the time since infall (TSI) of galaxies, obtained from the Yonsei Zoom-in Cluster Simulation, and the star formation rate (SFR) from the Sloan Digital Sky Survey Data Release 10 to study how quickly the star formation of disk galaxies is quenched in cluster environments. We first confirm that both simulated and observed galaxies are consistently distributed in phase space. We then hypothesize that the TSI and SFR are causally connected; thus, both the TSI and SFR of galaxies at each position of phase space can be associated through abundance matching. Using a flexible model, we derive the star formation history (SFH) of cluster galaxies that best reproduces the relationship between the TSI and SFR at z ∼ 0.08. According to this SFH, we find that galaxies with M * &gt; 109.5 M ⊙ generally follow the so-called “delayed-then-rapid” quenching pattern. Our main results are as follows: (i) part of the quenching takes place outside clusters through mass quenching and preprocessing. The e-folding timescale of this “ex situ quenching phase” is roughly 3 Gyr with a strong inverse mass dependence. (ii) The pace of quenching is maintained roughly for 2 Gyr (“delay time”) during the first crossing time into the cluster. During the delay time, quenching remains gentle, probably because gas loss happens primarily on hot and neutral gases. (iii) Quenching becomes more dramatic (e-folding timescale of roughly 1 Gyr) after delay time, probably because ram pressure stripping is strongest near the cluster center. Counterintuitively, more massive galaxies show shorter quenching timescales mainly because they enter their clusters with lower gas fractions due to ex situ quenching.

An excessively massive thick disc of the enormous edge-on lenticular galaxy NGC 7572

ABSTRACT Galactic discs are known to have a complex multilayer structure. An in-depth study of the stellar population properties of the thin and thick components can elucidate the formation and evolution of disc galaxies. Even though thick discs are ubiquitous, their origin is still debated. Here we probe the thick disc formation scenarios by investigating NGC 7572, an enormous edge-on galaxy having R25 ≈ 25 kpc and Vrot ≈ 370 km s−1, which substantially exceeds the Milky Way size and mass. We analysed DECaLS archival imaging and found that the disc of NGC 7572 contains two flaring stellar discs (a thin and a thick disc) with similar radial scales. We collected deep long-slit spectroscopic data using the 6 m Russian BTA telescope and analysed them with a novel technique. We first reconstructed a non-parametric stellar line-of-sight velocity distribution along the radius of the galaxy and then fitted it with two kinematic components accounting for the orbital distribution of stars in thin and thick discs. The old thick disc turned out to be 2.7 times as massive as the intermediate-age thin component, 1.6 × 1011 M⊙ versus 5.9 × 1010 M⊙, which is very unusual. The different duration of the formation epochs evidenced by the [Mg/Fe] values of +0.3 and +0.15 dex for the thick and thin discs respectively, their kinematics, and the mass ratio suggest that in NGC 7572 we observe a rapidly formed very massive thick disc and an underdeveloped thin disc, whose growth ended prematurely due to the exhaustion of the cold gas likely because of environmental effects.

The Formation of Exponential Disk Galaxies in MOND

Abstract The formation and evolution of galaxies are highly dependent on the dynamics of stars and gas, which is governed by the underlying law of gravity. To investigate how the formation and evolution of galaxies take place in Milgromian gravity (MOND), we present full hydrodynamical simulations with the Phantom of Ramses code. These are the first-ever galaxy formation simulations done in MOND with detailed hydrodynamics, including star formation, stellar feedback, radiative transfer, and supernovae. These models start from simplified initial conditions, in the form of isolated, rotating gas spheres in the early universe. These collapse and form late-type galaxies obeying several scaling relations, which was not a priori expected. The formed galaxies have a compact bulge and a disk with exponentially decreasing surface mass density profiles and scale lengths consistent with observed galaxies, as well as vertical stellar mass distributions with distinct exponential profiles (thin and thick disk). This work thus shows for the first time that disk galaxies with exponential profiles in both gas and stars are a generic outcome of collapsing gas clouds in MOND. These models have a slight lack of stellar angular momentum because of their somewhat compact stellar bulge, which is connected to the simple initial conditions and the negligible later gas accretion. We also analyze how the addition of more complex baryonic physics changes the resulting main properties of the models and find this to be negligibly so in the Milgromian framework.

Toward a new understanding of disk galaxy formation

AbstractOne of the most important open issues in astronomy is the assembly of galactic disks. Over the last decade this has been addressed with large surveys of the internal kinematics of galaxies spanning the last 10 billion years of the universe. I will discuss recent results from the field that show the kinematic assembly of disk galaxies since a redshift of 2.5, including recent deep 10–30 hour observations by my group with the DEIMOS spectrograph on Keck. These results strongly challenge traditional analytic models of galaxy formation and provide an important benchmark for simulations. Furthermore, I will discuss our plans for extending measurements to higher redshifts with future instruments such as the JWST's NIRSpec IFU and the E-ELT's MOSAIC and HARMONI IFUs. From mock JWST and E-ELT observations of simulated galaxies, we are learning that interpreting these observations of galaxies in the early universe, when merging is frequent, is not necessarily straightforward.