Question How do stars form?

[Harry Costas]

If stars are sucked into supermassive Condensates (Black Holes). We know they form Dipolar Electromagnetic Vortices and it is possible to expel such matter along the vortices. This matter engages in the formation of stars.
M87 is an elliptical Galaxy far greater than Andromeda and the Milky way combined, M87 jets have millions of stars within the vortices.

[Submitted on 6 Feb 2024 (v1), last revised 12 Apr 2024 (this version, v2)]

Multiphase gas in elliptical galaxies: the role of Type Ia supernovae​

Rajsekhar Mohapatra, Eliot Quataert

Massive elliptical galaxies harbor large amounts of hot gas (T≳106 K) in their interstellar medium (ISM) but are typically quiescent in star formation. Active-galactic nuclei (AGNs) jets and Type Ia supernovae (SNIa) inject energy into the ISM which offsets its radiative losses and keeps it hot. SNIa deposit their energy locally within the galaxy compared to the larger few×10 kpc-scale AGN jets. In this study, we perform high-resolution (5123) hydrodynamic simulations of a local (1 kpc3) density-stratified patch of massive galaxies' ISM. We include radiative cooling and shell-averaged volume heating, as well as randomly exploding SNIa. We study the effect of different fractions of supernova heating (with respect to the net cooling rate), different initial ISM density/entropy (which controls the thermal-instability growth time tti) and different degrees of stratification (which affects the free-fall time tff). We find that the SNIa drive predominantly compressive turbulence in the ISM with a velocity dispersion σv up to 40 kms−1 and logarithmic density dispersion σs∼0.2--0.4. These fluctuations trigger multiphase condensation in regions of the ISM where min(tti)/tff≲0.6exp(6σs), in agreement with theoretical expectations that large density fluctuations efficiently trigger multiphase gas formation. Since the SNIa rate is not self-adjusting, when the net cooling drops below the net heating rate the SNIa drive a hot wind which sweeps out most of the mass in our local model. Global simulations are required to assess the ultimate fate of this gas.

 

[Harry Costas]

I do not agree with this paper.
But! interesting to read.


[Submitted on 28 May 2024]

Magnetic Braneworlds: Cosmology and Wormholes​

Stefano Antonini, Luis Gabriel C. Bariuan

We construct 4D flat Big Bang-Big Crunch cosmologies and Anti-de Sitter (AdS) planar eternally traversable wormholes using braneworlds embedded in asymptotically AdS5 spacetimes. The background geometries are the AdS5 magnetic black brane and the magnetically charged AdS5 soliton, respectively. The two setups arise from different analytic continuations of the same saddle of the gravitational Euclidean path integral, in which the braneworld takes the form of a Maldacena-Maoz Euclidean wormhole. We show the existence of a holographic dual description of this setup in terms of a microscopic Euclidean boundary conformal field theory (BCFT) on a strip. By analyzing the BCFT Euclidean path integral, we show that the braneworld cosmology is encoded in a pure excited state of a CFT dual to a black brane microstate, whereas the braneworld wormhole is encoded in the ground state of the BCFT. The latter confines in the IR, and we study its confining properties using holography. We also comment on the properties of bulk reconstruction in the two Lorentzian pictures and their relationship via double analytic continuation. This work can be interpreted as an explicit, doubly-holographic realization of the relationship between cosmology, traversable wormholes, and confinement in holography, first proposed in arXiv:2102.05057, arXiv:2203.11220.

 

[Harry Costas]

Star formation is important because it allows to understand the workings of the universe.


[Submitted on 26 Apr 2024]

Inefficient star formation in high Mach number environments. II. Numerical simulations and comparison with analytical models​

Noé Brucy, Patrick Hennebelle, Tine Colman, Ralf S. Klessen, Corentin Le Yhuelic

Predicting the star formation rate (SFR) in galaxies is crucial to understand their evolution and morphology. To do so requires a fine understanding of how dense structures of gas are created and collapse. In that, turbulence and gravity play a major role. Within the gravo-turbulent framework, we assume that turbulence shapes the ISM, creating density fluctuations that, if gravitationally unstable, will collapse and form stars. The goal of this work is to quantify how different regimes of turbulence, characterized by the strength and compressibility of the driving, shape the density field. We are interested in the outcome in terms of SFR and how it compares with existing analytical models for the SFR. We run a series of hydrodynamical simulations of turbulent gas. The simulations are first conducted without gravity, so that the density and velocity are shaped by the turbulence driving. Gravity is then switched on, and the SFR is measured and compared with analytical models. The physics included in these simulations is very close to the one assumed in the classical gravo-turbulent SFR analytical models, which makes the comparison straightforward. We found that the existing analytical models convincingly agree with simulations at low Mach number, but we measure a much lower SFR in the simulation with a high Mach number. We develop, in a companion paper, an updated physically-motivated SFR model that reproduces well the inefficient high Mach regime of the simulations. Our work demonstrates that accurate estimations of the turbulent-driven replenishment time of dense structures and the dense gas spatial distribution are necessary to correctly predict the SFR in the high Mach regime. The inefficient high-Mach regime is a possible explanation for the low SFR found in dense and turbulent environments such as the centers of our Milky Way and other galaxies.

 

[Harry Costas]

For those that want to read.
Reseach keeps moving forward. Sometime one step back and then forward.

[Submitted on 14 May 2024]

The evolution of stellar X-ray activity and angular momentum as seen by eROSITA, TESS, and Gaia​

Keivan G. Stassun (1), Marina Kounkel (2) ((1) Vanderbilt University, (2) University of North Florida)

We have assembled a sample of ∼8200 stars with spectral types F5V-M5V, all having directly measured X-ray luminosities from eROSITA and rotation periods from TESS, and having empirically estimated ages via their membership in stellar clusters and groups identified in Gaia astrometry (ages 3-500 Myr). This is the largest such study sample yet assembled for the purpose of empirically constraining the evolution of rotationally driven stellar X-ray activity. We observe rotation-age-activity correlations that are qualitatively as expected: stars of a given spectral type spin down with age and they become less X-ray active as they do so. We provide simple functional representations of these empirical relationships that predict X-ray luminosity from basic observables to within 0.3 dex. Interestingly, we find that the rotation-activity relationship is far simpler and more monotonic in form when expressed in terms of stellar angular momentum instead of rotation period. We discuss how this finding may relate to the long-established idea that rotation-activity relationships are mediated by stellar structure (e.g., convective turnover time, surface area). Finally, we provide an empirical relation that predicts stellar angular momentum from basic observables, and without requiring a direct measurement of stellar rotation, to within 0.5 dex.

 

[Harry Costas]

Star formation is important in finding how they are produced in large numbers.

[Submitted on 8 May 2024]

A Gamma-ray Emitting Collisional Ring Galaxy System in our Galactic Neighborhood​

Vaidehi S. Paliya, D. J. Saikia (IUCAA)

The astrophysical γ-ray photons carry the signatures of the violent phenomena happening on various astronomical scales in our Universe. This includes supernova remnants, pulsars, and pulsar wind nebulae in the Galactic environment and extragalactic relativistic jets associated with active galactic nuclei (AGN). However, ∼30\% of the \gm-ray sources detected with the Fermi Large Area Telescope lack multiwavelength counterpart association, precluding us from characterizing their origin. Here we report, for the first time, the association of a collisional ring galaxy system in our Galactic neighborhood (distance ∼10 Mpc), formed as a consequence of a smaller `bullet' galaxy piercing through a larger galaxy, as the multi-frequency counterpart of an unassociated γ-ray source 4FGL~J1647.5−5724. The system, also known as "Kathryn's Wheel", contains two dwarf irregular galaxies and an edge-on, late-type, spiral galaxy surrounded by a ring of star-forming knots. We utilized observations taken from the Neil Gehrels Swift observatory, Rapid ASKAP Continuum Survey, SuperCOSMOS Hα Survey, Dark Energy Survey, and Visible MultiObject Spectrograph at Very Large Telescope to ascertain the association with 4FGL~J1647.5−5724 and to explore the connection between the star-forming activities and the observed γ-ray emission. We found that star-formation alone cannot explain the observed γ-ray emission, and additional contribution likely from the pulsars/supernova remnants or buried AGN is required. We conclude that arcsecond/sub-arcsecond-scale observations of this extraordinary γ-ray emitting galaxy collision will be needed to resolve the environment and explore the origin of cosmic rays.

 

[Harry Costas]

Star formation rates (SFR) is important to keep researching and their relation to Active Galactic Nuclei (AGN)

[Submitted on 15 May 2024]

Active Galactic Nuclei and STaR fOrmation in Nearby Galaxies (AGNSTRONG). I. Sample and Strategy​

Huynh Anh N. Le, Chen Qin, Yongquan Xue, Shifu Zhu, Kim Ngan N. Nguyen, Ruisong Xia, Xiaozhi Lin

We introduce our project, AGNSTRONG (Active Galactic Nuclei and STaR fOrmation in Nearby Galaxies). Our research goals encompass investigating the kinematic properties of ionized and molecular gas outflows, understanding the impact of AGN feedback, and exploring the coevolution dynamics between AGN strength activity and star formation activity. We aim to conduct a thorough analysis to determine whether there is an increase or suppression in SFRs among targets with and without powerful relativistic jets. Our sample consists of 35 nearby AGNs with and without powerful relativistic jet detections. Utilizing sub-millimeter (sub-mm) continuum observations at 450 {\mu}m and 850 {\mu}m from SCUBA-2 at the James Clerk Maxwell Telescope, we determine star-formation rates (SFRs) for our sources using spectral energy distribution (SED) fitting models. Additionally, we employ high-quality, spatially resolved spectra from UV-optical to near-infrared bands obtained with the Double Spectrograph and Triple Spectrograph mounted on the 200-inch Hale telescope at Palomar Observatory to study their multiphase gas outflow properties. This paper presents an overview of our sample selection methodology, research strategy, and initial results of our project. We find that the SFRs determined without including the sub-mm data in the SED fitting are overestimated by approximately 0.08 dex compared to those estimated with the inclusion of sub-mm data. Additionally, we compare the estimated SFRs in our work with those traced by the 4000Å break, as provided by the MPA-JHU catalog. We find that our determined SFRs are systematically higher than those traced by the 4000Å break. Finally, we outline our future research plans.

 

[Harry Costas]

Star Formation has been part of a cyclic event.
Yes we do have star births and star deaths.
This does not imply creating or destroying matter or energy.


[Submitted on 7 Aug 2024]

Signatures of mass segregation from competitive accretion and monolithic collapse​

Richard J. Parker (1), Emily J. Pinson (1), Hayley L. Alcock (1), James E. Dale (2) (1. University of Sheffield, UK, 2. Universitet Uppsala, Sweden)

The two main competing theories proposed to explain the formation of massive (>10M⊙) stars -- competitive accretion and monolithic core collapse -- make different observable predictions for the environment of the massive stars during, and immediately after, their formation. Proponents of competitive accretion have long predicted that the most massive stars should have a different spatial distribution to lower-mass stars, either through the stars being mass segregated, or being in areas of higher relative densities, or sitting deeper in gravitational potential wells. We test these predictions by analysing a suite of SPH simulations where star clusters form massive stars via competitive accretion with and without feedback. We find that the most massive stars have higher relative densities, and sit in deeper potential wells, only in simulations in which feedback is not present. When feedback is included, only half of the simulations have the massive stars residing in deeper potential wells, and there are no other distinguishing signals in their spatial distributions. Intriguingly, in our simple models for monolithic core collapse, the massive stars may also end up in deeper potential wells, because if massive cores fragment the stars are still massive, and dominate their local environs. We find no robust diagnostic test in the spatial distributions of massive stars that can distinguish their formation mechanisms, and so other predictions for distinguishing between competitive accretion and monolithic collapse are required.

 

[Harry Costas]

One must explain the billions of stars in the Milky Way's spiral arms.
BB nucleosynthesis explains how the stars were pumped out of a Black Hole (Condensate that mimics Black Hole Properties) from Condensate droplets.

[Submitted on 10 Jul 2024]

Rising from the Ashes: How the Milky Way Got Its Scars​

Angus Beane

The elemental abundance distribution of stars encodes the history of the gas-phase abundance in the Milky Way. Without a large, unbiased sample of highly precise stellar ages, the exact timing and nature of this history must be inferred from the abundances. In the two-dimensional plane of [alpha/Fe]-[Fe/H], it is now clear that two separate populations exist -- the low-alpha and high-alpha sequences. Structure in the elemental abundance distribution can arise from many processes -- proposals include specific gas infall scenarios, radial migration, high-redshift clump formation, and various effects associated with galaxy mergers, among others. In this work, we demonstrate another possible avenue for structure formation with clear observational predictions. In this scenario, the Galaxy underwent a starburst followed by a brief (hundreds of Myr) quiescent phase -- i.e., the Galaxy underwent a post-starburst rejuvenation sequence at z~2. A natural consequence of the quiescent phase is that stars in the valley of the bimodality do not form because: (1) the absence of enrichment from high-mass stars leads to a rapid reduction in [alpha/Fe], and (2) any time the gas spends in the abundance valley is deemphasized in the present day distribution because the star formation rate is lower. With a set of idealized merger simulations, we demonstrate the feasibility of this proposal. This "phoenix hypothesis" predicts a ~300 Myr gap in stellar ages at a fixed [Fe/H] and that stars which form directly after this gap would have lower [alpha/Fe] than stars which form slightly (~1 Gyr) later.

 

[Harry Costas]

It's an exciting time to study star formations.
Sometimes we need to get out of our ways.

[Submitted on 10 Jul 2024]

Overview Results of JWST Observations of Star-Forming Clusters in the Extreme Outer Galaxy​

Natsuko Izumi, Michael E. Ressler, Ryan M. Lau, Patrick M. Koch, Masao Saito, Naoto Kobayashi, Chikako Yasui

The extreme outer Galaxy (EOG), which we define as the region of the Milky Way with a galactocentric radius of more than 18 kpc, provides an excellent opportunity to study star formation in an environment significantly different from that in the solar neighborhood because of its lower metallicity and lower gas density. We carried out near- and mid-infrared (NIR and MIR) imaging observations toward two star-forming clusters located in the EOG using JWST NIRCam and MIRI with nine filters: F115W, F150W, F200W, F350W, F405N, F444W, F770W, F1280W, and F2100W. In this paper, we present an overview of the observations, data reduction, and initial results. The NIR sensitivity is approximately 10--80 times better than our previous observation with the Subaru 8.2 m telescope. Accordingly, the mass detection limit reaches to about 0.01--0.05 M⊙, which is about 10 times better than the previous observations. At MIR wavelengths, the high sensitivity and resolution data enable us to resolve individual young stellar objects in such a distant region for the first time. The mass detection limit at MIR F770W filter reaches about 0.1--0.3 M⊙. With these new observations, we have identified components of the clusters that previous surveys did not detect, including class 0 candidates, outflow/jet components, and distinctive nebular structures. These data will enable us to investigate the properties of star formation in the EOG at the same depth of detail as previous observations of star formation in the solar neighborhood.

 

[Harry Costas]

Star formation from jets.

[Submitted on 15 Jul 2024 (v1), last revised 19 Aug 2024 (this version, v4)]

What halts the growth of galaxies?​

Johannes Buchner

The gas reservoir of galaxies can be altered by outflows driven by star-formation and luminous active galactic nuclei. Jets heating the surroundings of host galaxies can also prevent gas cooling and inflows. Spectacular examples for these three mass displacement channels have been observed, but their importance in transforming the galaxy population depends on the occurrence rates of outflow triggers. We aim to investigate the absolute and relative importance of these three channels. In an observation-driven approach, we combine distribution functions and scaling relations to empirically compare average outflow rates across the galaxy total stellar mass spectrum and across cosmic time. This hinges on local outflow studies which should be extended to systematic, large and diverse samples, and we do not yet consider a halo heating effect by radiation-driven outflows. Our results show, independent of simulations, the dominance of star formation-driven outflows in low-mass galaxies. Massive galaxies today are predominately prevented from growing further by jet heating, while at z=1−3 all three processes are approximately similarly important. Over the full mass spectrum and cosmic history, outflows driven by the radiation from active galactic nuclei is never the dominant process.

 

[Harry Costas]

Sorry for posting so many papers.
I do not want my opinion to affect the way you read these papers.
Sometimes I cannot hold myself back.

[Submitted on 21 Aug 2024]

Global Preventive Feedback of Powerful Radio Jets on Galaxy Formation​

Renyue Cen (Zhejiang University)

Firmly anchored on observational data, giant radio lobes from massive galaxies hosting supermassive black holes can exert a major negative feedback effect, by endowing the intergalactic gas with significant magnetic pressure hence retarding or preventing gas accretion onto less massive halos in the vicinity. Since massive galaxies that are largely responsible for producing the giant radio lobes, this effect is expected to be stronger in more overdense large-scale environments, such as proto-clusters, than in underdense regions, such as voids. We show that by redshift z=2 halos with masses up to $(10^{11-12}, 10^{12-13})\msun$ are significantly hindered from accreting gas due to this effect for radio bubble volume filling fraction of (1.0,0.2), respectively. Since the vast majority of the stars in the universe at z<2−3 form precisely in those halos, this negative feedback process is likely one major culprit for causing the global downturn in star formation in the universe since. It also provides a natural explanation for the rather sudden flattening of the slope of the galaxy rest-frame UV luminosity function around z∼2. A cross-correlation between proto-clusters and Faraday rotation measures may test the predicted magnetic field. Inclusion of this external feedback process in the next generation of cosmological simulations may be imperative.

 

[Harry Costas]

View: https://youtu.be/GTcbas5usK4?si=6jOamJhPSsXRk0ZJ


This is a prime example of how billions of stars formed along the dipolar jets that extend to about 23 million light years.

The jets are not thin. At the start they may be a few light days and at the end millions of light years across.

 

[Harry Costas]

Have you ever wondered why most of the stars in the Milky Way are in spiral arms?

 

[Harry Costas]

If stars are formed through compaction.
How do you explain star formation from BBT Nucleosynthesis from a condensate?

[Submitted on 11 Oct 2024]

Visual Orbits of Wolf-Rayet Stars I: The Orbit of the dust-producing Wolf-Rayet binary WR\,137 measured with the CHARA Array​

Noel D. Richardson, Gail H. Schaefer, Jan J. Eldridge, Rebecca Spejcher, Amanda Holdsworth, Ryan M. Lau, John D. Monnier, Anthony F. J. Moffat, Gerd Weigelt, Peredur M. Williams, Stefan Kraus, Jean-Baptiste Le Bouquin, Narsireddy Anugu, Sorabh Chhabra, Isabelle Codron, Jacob Ennis, Tyler Gardner, Mayra Gutierrez, Noura Ibrahim, Aaron Labdon, Cyprien Lanthermann, Benjamin R. Setterholm

Classical Wolf-Rayet stars are the descendants of massive OB stars that have lost their hydrogen envelopes and are burning helium in their cores prior to exploding as type Ib/c supernovae. The mechanisms for losing their hydrogen envelopes are either through binary interactions or through strong stellar winds potentially coupled with episodic mass-loss. Amongst the bright classical WR stars, the binary system WR\,137 (HD\,192641; WC7d + O9e) is the subject of this paper. This binary is known to have a 13-year period and produces dust near periastron. Here we report on interferometry with the CHARA Array collected over a decade of time and providing the first visual orbit for the system. We combine these astrometric measurements with archival radial velocities to measure masses of the stars of MWR=9.5±3.4M⊙ and MO=17.3±1.9M⊙ when we use the most recent \textit{Gaia} distance. These results are then compared to predicted dust distribution using these orbital elements, which match the observed imaging from \textit{JWST} as discussed recently by Lau et al. Furthermore, we compare the system to the BPASS models, finding that the WR star likely formed through stellar winds and not through binary interactions. However, the companion O star did likely accrete some material from the WR's mass-loss to provide the rotation seen today that drives its status as an Oe star.

 

[Harry Costas]

I would encourage self-research in the field.
Opinions are good, but! facts and evidence are the best.

[Submitted on 16 Oct 2024 (v1), last revised 17 Oct 2024 (this version, v2)]

The Milky Way atlas for linear filaments II. clump rotation versus filament orientation​

Xuefang Xu, Ke Wang, Qian Gou, Tapas Baug, Di Li, Chunguo Duan, Juncheng Lei

Dense clumps distributed along filaments are the immediate medium for star formation. Kinematic properties of the clumps, such as velocity gradient and angular momentum, combined with filament orientation, provide important clues to the formation mechanism of filament-clump configurations and the role of filaments in star formation. By cross-matching the Milky Way atlas for linear filaments and the Structure, Excitation and Dynamics of the Inner Galactic Interstellar Medium (SEDIGISM) 13CO (2-1) data, we aim to derive the velocity gradient and its direction, the specific angular momentum (J/M), and the ratio (\beta) between the rotational energy and gravitational energy of clumps, as well as to investigate the alignment between clump rotation and filament orientation. We found a monotonic increase in J/M as a function of clump size (R), following a power-law relation J/M~\propto~R^{1.5\pm0.2}. The ratio \beta ranges from 1.1~\times~10^{-5} to 0.1, with a median value 1.0~\times~10^{-3}, suggesting that clump rotation provides insignificant support against gravitational collapse. The distribution of the angle between clump rotation and natal filament orientation is random, indicating that the clumps' rotational axes have no discernible correlation with the orientation of their hosting filaments. Counting only the most massive clump in each filament also finds no alignment between clump rotation and filament orientation.

 

[Harry Costas]

Interesting reading.
One issue is that they think along the lines of the BBT.
But! don't let that stop you, because of my opinion.

[Submitted on 16 Oct 2024]

The Star Formation History of Nearby Galaxies: A Machine Learning Approach​

Yujiao Yang, Chao Liu, Ming Yang, Yun Zheng, Hao Tian

Reproducing color-magnitude diagrams (CMDs) of star-resolved galaxies is one of the most precise methods for measuring the star formation history (SFH) of nearby galaxies back to the earliest time. The upcoming big data era poses challenges to the traditional numerical technique in its capacity to deal with vast amounts of data, which motivates us to explore the feasibility of employing machine learning networks in this field. In this study, we refine the synthetic CMD method with a state-of-the-art theoretical stellar evolution model to simulate the properties of stellar populations, incorporate the convolutional neural network (CNN) in the fitting process to enhance the efficiency, and innovate the initial stellar mass estimation to improve the flexibility. The fine-tuned deep learning network, named \texttt{SFHNet}, has been tested with synthetic data and further validated with photometric data collected from the Hubble Space Telescope (\textit{HST}). The derived SFHs are largely in accordance with those reported in the literature. Furthermore, the network provides detailed insights into the distribution of stellar density, initial stellar mass, and star formation rate (SFR) over the age-metallicity map. The application of the deep learning network not only measures the SFH accurately but also enhances the synthetic CMD method's efficiency and flexibility, thereby facilitating a more comprehensive and in-depth understanding of nearby galaxies.

 

[Harry Costas]

Star Formation from the start.

[Submitted on 31 Oct 2024]

High-velocity outflows persist up to 1 Gyr after a starburst in recently-quenched galaxies at z > 1​

Elizabeth Taylor, David Maltby, Omar Almaini, Michael Merrifield, Vivienne Wild, Kate Rowlands, Jimi Harrold

High-velocity outflows are ubiquitous in star-forming galaxies at cosmic noon, but are not as common in passive galaxies at the same epoch. Using optical spectra of galaxies selected from the UKIDSS Ultra Deep Survey (UDS) at z > 1, we perform a stacking analysis to investigate the transition in outflow properties along a quenching time sequence. To do this, we use MgII (2800 A) absorption profiles to investigate outflow properties as a function of time since the last major burst of star formation (tburst). We find evidence for high-velocity outflows in the star-forming progenitor population (vout ~ 1400 ± 210 km/s), for recently quenched galaxies with tburst < 0.6 Gyr (vout ~ 990 ± 250 km/s), and for older quenched galaxies with 0.6 < tburst < 1 Gyr (vout ~ 1400 ± 220 km/s). The oldest galaxies (tburst > 1 Gyr) show no evidence for significant outflows. Our samples show no signs of AGN in optical observations, suggesting that any AGN in these galaxies have very short duty cycles, and were 'off' when observed. The presence of significant outflows in the older quenched galaxies (tburst > 0.6 Gyr) is difficult to explain with starburst activity, however, and may indicate energy input from episodic AGN activity as the starburst fades.

 

[Harry Costas]

Star Formation.
How did Trillions of Stars within billions of Galaxies in a short period of time, if we look at the Big Bang Theory time scale.


[Submitted on 14 Nov 2024]

COSMOS2020: Disentangling the Role of Mass and Environment in Star Formation Activity of Galaxies at 0.4<z<4​

Sina Taamoli, Negin Nezhad, Bahram Mobasher, Faezeh Manesh, Nima Chartab, John R. Weaver, Peter L. Capak, Caitlin M. Casey, Ghassem Gozaliasl, Kasper E. Heintz, Olivier Ilbert, Jeyhan S. Kartaltepe, Henry J. McCracken, David B. Sanders, Nicholas Scoville, Sune Toft, Darach Watson

The role of internal and environmental factors in the star formation activity of galaxies is still a matter of debate, particularly at higher redshifts. Leveraging the most recent release of the COSMOS catalog, COSMOS2020, and density measurements from our previous study we disentangle the impact of environment and stellar mass on the star formation rate (SFR), and specific SFR (sSFR) of a sample of ∼210,000 galaxies within redshift range 0.4<z<4 and present our findings in three cosmic epochs: 1) out to z∼1, the average SFR and sSFR decline at extremely dense environments and high mass end of the distribution which is mostly due to the presence of the massive quiescent population; 2) at 1<z<2, the environmental dependence diminishes, while mass is still the dominant factor in star formation activity; 3) beyond z∼2, our sample is dominated by star-forming galaxies and we observe a reversal of the trends seen in the local universe: the average SFR increases with increasing environmental density. Our analysis shows that both environmental and mass quenching efficiencies increase with stellar mass at all redshifts, with mass being the dominant quenching factor in massive galaxies compared to environmental effects. At 2<z<4, negative values of environmental quenching efficiency suggest that the fraction of star-forming galaxies in dense environments exceeds that in less dense regions, likely due to the greater availability of cold gas, higher merger rates, and tidal effects that trigger star formation activity.

 

[Harry Costas]

Read this paper to your heart's content. Information is coming fast from many scientists.

[Submitted on 19 Nov 2024]

Galaxy Specific Star Formation Rate Is Independent of Halo Spin​

Zichen Hua, Yu Rong

Utilizing ALFALFA HI data, we investigate the relationship between specific star formation rate (sSFR) and halo spin across various star-forming galaxies. Our analysis reveals no significant correlation between sSFR and halo spin, irrespective of the galactic environment. Previous research suggests that high-spin halos tend to harbor extended, low-density stellar distributions due to suppressed gas cooling and star formation. However, unlike galaxy size and density, sSFR may primarily reflect the current star-forming state rather than long-term history, indicating potential independence from halo spin.

 

[Harry Costas]

Merry Xmas
To one and all

 

[Harry Costas]

I will keep on sharing papers that I read.
You draw your conclusions.

[Submitted on 14 Dec 2024]

Ultra Diffuse Dwarf Galaxies Hosting Pseudo-bulges​

Yu Rong, Hong-Xin Zhang, Cheng Cheng, Qi Guo, Weiyu Ding, Zichen Hua, Huiyuan Wang, Xu Kong

By analyzing data from DESI Legacy Imaging Survey of the dwarf galaxies in the Arecibo Legacy Fast Alfa Survey, we have identified five ultra-diffuse galaxies (UDGs) featuring central pseudo-bulges. These UDGs display blue pseudo-bulges with Sérsic indices n<2.5 and effective radii spanning 300-700 pc, along with bluer thin stellar disks exhibiting low surface brightness and expansive effective radii that align with the UDG definition. The rotation velocities of these UDGs, determined using HI line widths and optical inclinations, exceed those of most dwarf galaxies of similar mass, suggesting the high halo spins or substantial dark matter halos. We propose that these UDGs likely formed through mergers of dwarf galaxies lacking old stars in their progenitors, resulting in the development of central bulge-like structures during starbursts triggered by the mergers, while also enhancing their halo spin. Subsequent gas accretion facilitated the formation of extended stellar disks. It is also worth noting the possibility that these UDGs could alternatively represent ``failed L⋆ galaxies'' with massive dark matter halos but reduced star formation efficiencies. If future high-resolution HI observations confirm the presence of massive halos around these UDGs, they may have formed due to intense AGN feedback in the early universe, and may be the descendants of ``little red dots'' observed by the James Webb Space Telescope, which are characterized by heightened central black hole masses and intensified accretion and feedback processes in the early universe.