High Star Formation Rate Research Articles

Chemical Abundances in the Nuclear Star Cluster of the Milky Way: Alpha-element Trends and Their Similarities with the Inner Bulge

Abstract Chemical characterization of the Galactic center is essential for understanding its formation and structural evolution. Trends of alpha (α) elements, such as magnesium, silicon, and calcium, serve as powerful diagnostic tools, offering insights into star formation rates and gas-infall history. However, high extinction has previously hindered such studies. In this study, we present a detailed chemical abundance analysis of M giants in the Milky Way's nuclear star cluster (NSC), focusing on α-element trends with metallicity. High-resolution, near-infrared spectra were obtained using the Immersion GRating INfrared Spectrograph on the Gemini South telescope for nine M giants. Careful selection of spectral lines, based on a solar-neighborhood control sample of 50 M giants, was implemented to minimize systematic uncertainties. Our findings show enhanced α-element abundances in the predominantly metal-rich NSC stars, consistent with trends in the inner bulge. The NSC stars follow the high-[α/Fe] envelope seen in the solar vicinity's metal-rich population, indicating a high star formation rate. The α-element trends decrease with increasing metallicity, also at the highest metallicities. Our results suggest the NSC population likely shares a similar evolutionary history with the inner bulge, challenging the idea of a recent dominant star formation burst. This connection between the NSC and the inner-disk sequence suggests that the chemical properties of extragalactic NSCs of Milky Way–type galaxies could serve as a proxy for understanding the host galaxies’ evolutionary processes.

On the Formation of Planets in the Milky Way’s Thick Disk

Abstract Exoplanet demographic surveys have revealed that close-in (≲1 au) small planets orbiting stars in the Milky Way’s thick disk are ∼50% less abundant than those orbiting stars in the Galactic thin disk. One key difference between the two stellar populations is the time at which they emerged: thick-disk stars are the likely product of cosmic noon (redshift z ∼ 2), an era characterized by high star formation rate, massive and dense molecular clouds, and strong supersonic turbulence. Solving for the background radiation field in these early star-forming regions, we demonstrate that protoplanetary disks at cosmic noon experienced radiation fields up to ∼7 orders of magnitude more intense than in solar neighborhood conditions. Coupling the radiation field to a one-dimensional protoplanetary disk evolution model, we find that external UV photoevaporation destroys protoplanetary disks in just ∼0.2–0.5 Myr, limiting the timescale over which planets can assemble. Disk temperatures exceed the sublimation temperatures of common volatile species for ≳Myr timescales, predicting more spatial homogeneity in gas chemical composition. Our calculations imply that the deficit in planet occurrence around thick-disk stars should be even more pronounced for giant planets, particularly those at wide orbital separations, predicting a higher rocky-to-giant planet ratio in the Galactic thick disk versus thin disk.

Investigating the Star Formation Characteristics of Radio Active Galactic Nuclei

The coevolution of supermassive black holes and their host galaxies represents a fundamental question in astrophysics. One approach to investigating this question involves comparing the star formation rates (SFRs) of active galactic nuclei (AGNs) with those of typical star-forming galaxies. At relatively low redshifts (z ≲ 1), radio AGNs manifest diminished SFRs, indicating suppressed star formation, but their behavior at higher redshifts is unclear. To examine this, we leveraged galaxy and radio-AGN data from the well-characterized W-CDF-S, ELAIS-S1, and XMM-LSS fields. We established two mass-complete reference star-forming galaxy samples and two radio-AGN samples, consisting of 1763 and 6766 radio AGNs, the former being higher in purity and the latter more complete. We subsequently computed star-forming fractions (f SF; the fraction of star-forming galaxies to all galaxies) for galaxies and radio-AGN host galaxies and conducted a robust comparison between them up to z ≈ 3. We found that the tendency for radio AGNs to reside in massive galaxies primarily accounts for their low f SF, which also shows a strong negative dependence upon M ⋆ and a strong positive evolution with z. To investigate further the star formation characteristics of those star-forming radio AGNs, we constructed the star-forming main sequence (MS) and investigated the behavior of the position of AGNs relative to the MS at z ≈ 0–3. Our results reveal that radio AGNs display lower SFRs than star-forming galaxies in the low-z and high-M ⋆ regime and, conversely, exhibit comparable or higher SFRs than MS star-forming galaxies at higher redshifts or lower M ⋆.

FASHI: An Untargeted Survey of the 21 cm H i Absorption Galaxies with FAST

The FAST All Sky H I survey (FASHI) will cover the entire observable sky (∼22,000 square degrees) with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). With the currently released data, we perform an untargeted survey of 21 cm H i absorption galaxies at redshift z ≲ 0.09 over an area of about 10,000 square degrees. We have detected 51 H i absorbers, including 21 previously known and 30 new ones. The probability of occurrence for the H i absorbers in all H i galaxies is 1/1078. The radio flux densities of the FASHI absorbers are mainly concentrated in the range of S 1.4GHz = 10 ∼ 100 mJy, but also as low as 2.6 ± 0.4 mJy. We find that the host galaxies of the associated H i absorbers have relatively high star formation rates, and there is a negative correlation between the H i column density and the stellar mass in the host galaxy. Consequently, FAST has significantly improved the capabilities and performance for H i absorption observations and has provided a true untargeted survey of 21 cm H i absorption galaxies for such studies.

The connections among morphology, environment, and star formation with Galaxy Zoo Hubble

ABSTRACT Morphology is an important implication for studying the formation and evolution of galaxies. Previous studies have investigated the effects of spiral arms on star formation activities, but it is not clear how clumpy structure affects this process. In this work, we combine Galaxy Zoo Hubble project and 3D-HST/Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey programs to study the influence of morphological structure on star formation processes and the relationship between morphology and the environment at $0 \lt z \lt 1.0$. We find that galaxies with spiral arms and clumpy structures have higher star formation rates than smooth galaxies, and as the redshift decreases, this result remains unchanged. Analysis based on the subsamples, We find that stellar mass is related to the number of arms but not to the number of clumps. In addition, we do not find that an increase in the numbers of arms and/or clumps stimulates greater star formation. We also find that less-clump galaxies preferentially inhabit high-density environments, while more-clump galaxies preferentially inhabit low-density environments. This phenomenon is not significant in spiral galaxies. Our results show that environmental effects may have a greater influence on clumpy structures compared to spiral arm structures, which in turn affects the star formation activities of galaxies.

DESI Emission-line Galaxies: Unveiling the Diversity of [O ii] Profiles and Its Links to Star Formation and Morphology

We study the [O ii] profiles of emission-line galaxies (ELGs) from the Early Data Release of the Dark Energy Spectroscopic Instrument (DESI). To this end, we decompose and classify the shape of [O ii] profiles with the first two eigenspectra derived from principal component analysis. Our results show that DESI ELGs have diverse line profiles, which can be categorized into three main types: (1) narrow lines with a median width of ∼50 km s−1, (2) broad lines with a median width of ∼80 km s−1, and (3) two redshift systems with a median velocity separation of ∼150 km s−1, i.e., double-peak galaxies. To investigate the connections between the line profiles and galaxy properties, we utilize the information from the COSMOS data set and compare the properties of ELGs, including star formation rate (SFR) and galaxy morphology, with the average properties of reference star-forming galaxies with similar stellar mass, sizes, and redshifts. Our findings show that, on average, DESI ELGs have a higher SFR and more asymmetrical/disturbed morphology than the reference galaxies. Moreover, we uncover a relationship between the line profiles, the excess SFR, and the excess asymmetry parameter, showing that DESI ELGs with broader [O ii] line profiles have more disturbed morphology and higher SFR than the reference star-forming galaxies. Finally, we discuss possible physical mechanisms giving rise to the observed relationship and the implications of our findings on the galaxy clustering measurements, including the halo occupation distribution modeling of DESI ELGs and the observed excess velocity dispersion of the satellite ELGs.

High-resolution HI mapping of nearby extremely metal-poor blue compact dwarf galaxies

Aims. Optical observations of blue compact dwarf galaxies (BCDs) show they typically have high specific star formation rates (sSFRs) and low metallicites. A subset of these galaxies (those with the lowest gas phase metallicities) display cometary optical morphologies similar to those found at high redshift. Whether this combination of properties predominantly arises from interactions with neighbours or via accretion from the cosmic web, or is indeed due to something else, remains unclear. Our aim is to use high-resolution H I mapping to gain insights into the processes driving the observed properties of a sample of extremely metal-poor (XMP) BCDs. Methods. We present Very Large Array B– and C–configuration H I mapping of the four BCDs of our sample. For three of the targeted BCDs, we also detected and mapped the H I in their nearby companions. Results. In these three cases, there is H I morphological and kinematic evidence of a recent flyby interaction between the BCD and a nearby companion galaxy. The H I evidence for recent interactions for these three BCDs is corroborated by our analysis of the tidal forces exerted on the BCDs by companions with available spectroscopic redshifts. In one of these cases, J0204–1009, we obtain sufficient spatial resolution to determine that the BCD is dominated by dark matter (DM) and estimate its DM halo mass to be in the range of 1.2 × 1011 to 5.2 × 1011 M⊙. However, it is the most isolated BCD in our small sample, J0301–0052, that shows one of the most asymmetric H I morphologies. J0301–0052 has a similar cometary H I morphology to its optical morphology, although the H I column density maximum is projected at the end of the optical tail. Conclusion. Our H I observations suggest that J0301–0052 may be undergoing a merger, while the other members of our BCD sample show evidence of a recent tidal interaction with a near neighbour. While our selection criteria favour BCDs with companions, our results are consistent with previous literature showing that most BCDs are associated with either mild tidal interactions or mergers.

FAST H i 21 cm Study of Blueberry Galaxies

Green Peas (GPs) and blueberry galaxies (BBs) are thought to be local analogs (z < 0.1) of high redshift Lyα emitters. H i study of these can help us understand the star formation in the primordial Universe. In this Letter, we present the results of H i 21 cm study of 28 high specific star formation rate (sSFR ≳ 10−8yr −1) BBs at z ≲ 0.05 with the Five-hundred-meter Aperture Spherical radio Telescope. We report significant H i detection towards two BBs, namely J1026+0426 and J1132+0809, and discuss possible H i contribution from neighboring galaxies. The median 3σ upper limit of ∼2.0 × 108 M ⊙ was obtained on H i mass for galaxies with nondetections. We find BBs tend to have lower H i-to-stellar-mass ratio or gas fraction (f H i ) than expected from f H i –sSFR and f H i –M * relations for main-sequence galaxies. The BBs also have a median 3σ upper limit on H i gas depletion timescale (τ H i ) ∼ 0.5 Gyr, about 1 order of magnitude lower than τ H i for local main-sequence galaxies. We find a significantly low H i detection rate of 2/28 (7.1 −4.6+9.4 %) towards these galaxies, which is similar to previous H i studies of low redshift GPs of high ionization parameter indicator, O32 ≡ O[iii]λ5007/O[ii]λ3727 ratios ≳10.

Ionized Carbon in Galaxies: The [C ii] 158 μm Line as a Total Molecular Gas Mass Tracer Revisited

In this paper, we present a statistical study of the [C ii] 158 μm line and the CO(1−0) emission for a sample of ∼200 local and high-z (32 sources with z > 1) galaxies with very different physical conditions. We explore the correlation between the luminosities of [C ii] and CO(1−0) lines and obtain a strong linear relationship, confirming that [C ii] is able to trace total molecular gas mass, with a small difference between (U)LIRGs and less-luminous galaxies. The tight and linear relation between [C ii] and CO(1−0) is likely determined by the average value of the observed visual extinction A V and the range of G 0/n in galaxies. Further investigations into the dependence of L [C ii]/L CO(1−0) on different physical properties show that L [C ii]/L CO(1−0) (1) anticorrelates with ΣIR, and the correlation becomes steeper when ΣIR ≳ 1011 L ⊙ kpc−2; (2) correlates positively with the distance from the main sequence Δ(MS) when Δ(MS) ≲ 0; and (3) tends to show a systematically smaller value in systems where the [C ii] emission is dominated by ionized gas. Our results imply that caution needs to be taken when applying a constant [C ii]-to-M mol conversion factor to estimate the molecular gas content in extreme cases, such as galaxies having low-level star formation activity or high star formation rate surface density.

Radio-AGN activity across the galaxy population: dependence on stellar mass, star formation rate, and redshift

ABSTRACT We characterize the co-evolution of radio-loud active galactic nuclei (AGN) and their galaxies by mapping the dependence of radio-loud AGN activity on stellar mass and star formation rate (SFR) across cosmic time (out to $z \sim 1.5$). Deep LOFAR radio observations are combined with large galaxy samples to study the incidence of radio-loud AGN across the galaxy population; the AGN are further split into low-excitation radio galaxies (LERGs) and high-excitation radio galaxies (HERGs). We find that LERG activity occurs over a wide range of SFRs, whereas HERGs are typically found in galaxies with ongoing star formation. The LERGs are then split based on their SFRs relative to the main sequence, across redshift. Within quiescent galaxies, LERG activity shows a steep stellar mass dependence with the same normalization across the past $\sim$10 Gyr; this indicates that hot gas fuels LERGs in quiescent galaxies across cosmic time. In massive galaxies [$\log _{10}(M/\rm {{\rm M}_{\odot }}) \gtrsim 11$], the incidence of LERGs is roughly constant across the galaxy population, suggesting that LERGs in massive galaxies may be fuelled by hot gas regardless of the star formation activity. At lower masses, however, LERG activity is significantly more enhanced (by a factor of up to 10) in star-forming galaxies compared to quiescent galaxies; this suggests that an additional fuelling mechanism, likely associated with cold gas, may fuel the LERGs in galaxies with higher SFRs. We find that HERGs typically accrete above 1 per cent of the Eddington-scaled accretion rate, and the LERGs typically accrete below this level.

INTEGRAL search for magnetar giant flares from the Virgo Cluster and in nearby galaxies with high star formation rate

Abstract Giant flares from magnetars can reach, for a fraction of a second, luminosities greater than 1047 erg s−1 in the hard X-ray/soft γ-ray range. This makes them visible at distances of several megaparsecs. However, at extragalactic distances (farther than the Magellanic Clouds) they are difficult to distinguish from the short γ-ray bursts, which occur much more frequently. Since magnetars are young neutron stars, nearby galaxies with a high rate of star formation are optimal targets to search for magnetar giant flares (MGFs). Here we report the results of a search for MGFs in observations of the Virgo cluster and in a small sample of nearby galaxies obtained with the IBIS instrument on the INTEGRAL satellite. From the currently known MGF sample we find that their energy distribution is well described by a power law with slope γ=2 (with 90 per cent c.l. interval [1.7-2.2]). From the lack of detections in this extensive data set (besides 231115A in M82) we derive a 90 per cent c.l. upper limit on the rate of MGF with E &amp;gt; 3 × 1045 erg of ∼2 × 10−3 yr−1 per magnetar and a lower limit of R(E) &amp;gt; ∼4 × 10−4 yr−1 magnetar−1 for E &amp;lt; 1045 erg.

Witnessing an extreme, highly efficient galaxy formation mode with resolved Lyman-α and Lyman-continuum emission

J1316+2614 at z = 3.613 is the UV-brightest (MUV = −24.7) and strongest Lyman continuum-emitting (fescLyC ≈ 90%) star-forming galaxy known; it also shows signatures of inflowing gas from its blue-dominated Lyα profile. We present high-resolution imaging with the Hubble Space Telescope (HST) and the Very Large Telescope (VLT) of the LyC, Lyα, rest-UV, and optical emission of J1316+2614. Detailed analysis of the LyC and UV light distributions reveals compact yet resolved profiles, with LyC and UV morphologies showing identical half-light radii of reff ≃ 220 pc. The continuum-subtracted Lyα emission, obtained with the HST ramp-filter FR551N, reveals an extended filamentary structure of ≃6.0 kpc oriented south to north with only residual flux within the stellar core, suggesting a Lyα ‘hole’. Our spectral energy distribution analysis shows that J1316+2614 is characterised by a young (5.7 ± 1.0 Myr), nearly un-obscured stellar population with a high star-formation rate (SFR = 898 ± 181 M⊙ yr−1) and a stellar mass of M⋆young = (4.8 ± 0.3) × 109 M⊙. Additionally, the spectral energy distribution analysis supports the absence of an underlying old stellar population (M⋆old ≤ 2.8 × 109 M⊙, 3σ). J1316+2614 presents remarkably high SFR and stellar mass surface densities of log(Σ SFR[M⊙ yr−1 kpc−2]) = 3.47 ± 0.11 and log(ΣM⋆[M⊙pc−2]) = 4.20 ± 0.06, respectively, which are among the highest observed in star-forming galaxies and are more typically observed in local young massive star clusters and globular clusters. Our findings indicate that J1316+2614 is a powerful, young, and compact starburst that is leaking a significant amount of LyC photons due to a lack of gas and dust within the starburst. We explored the conditions for gas expulsion using a simple energetic balance and find that, given the strong binding force in J1316+2614, a high star-formation efficiency (ϵSF ≥ 0.7) is necessary to explain the removal of gas and its exposed nature. Our results thus suggest a close link between high ϵSF and high fescLyC. This high efficiency can also naturally explain the remarkably high SFR, UV luminosity, and efficient mass growth of J1316+2614, which acquired at least 62% of its mass in the last 6 Myr. J1316+2614 may exemplify an intense, feedback-free starburst with a high ϵSF, similar to those proposed for UV-bright galaxies at high redshifts.

X-ray observations of Blueberry galaxies

Context. Compact star-forming galaxies were dominant galaxy types in the early Universe. Blueberry galaxies (BBs) represent their local analogues, being very compact and having intense star formation. Aims. Motivated by high X-ray emission recently found in other analogical dwarf galaxies, called Green Peas, we probed the X-ray properties of BBs to determine if their X-ray emission is consistent with the empirical laws for star-forming galaxies. Methods. We performed the first X-ray observations of a small sample of BBs with the XMM-Newton satellite. Spectral analysis for detected sources and upper limits measured via Bayesian-based analysis for very low-count measurements were used to determine the X-ray properties of our galaxy sample. Results. Clear detection was obtained for only two sources, with one source exhibiting an enhanced X-ray luminosity to the scaling relations. For the remaining five sources, only an upper limit was constrained, suggesting BBs to be rather underluminous as a whole. Our analysis shows that the large scatter cannot be easily explained by the stochasticity effects. While the bright source is above (and inconsistent with) the expected distribution at almost the 99% confidence level, the upper limits of the two sources are below the expected distribution. Conclusions. These results indicate that the empirical relations between the star formation rate, metallicity, and X-ray luminosity might not hold for BBs with uniquely high specific star formation rates. One possible explanation could be that the BBs may not be old enough to have a significant X-ray binary population. The high luminosity of the only bright source can then be caused by an additional X-ray source, such as a hidden active galactic nucleus or more extreme ultraluminous X-ray sources.

The host of GRB 171205A in 3D

Long GRB hosts at z &lt; 1 are usually low-mass, low-metallicity star-forming galaxies. Here we present the most detailed, spatially resolved study of the host of GRB 171205A so far, a grand-design barred spiral galaxy at z = 0.036. Our analysis includes MUSE integral field spectroscopy complemented with high-spatial-resolution UV/VIS HST imaging and CO(1−0) and H I 21 cm data. The GRB is located in a small star-forming region in a spiral arm of the galaxy at a deprojected distance of ∼8 kpc from the center. The galaxy shows a smooth negative metallicity gradient and the metallicity at the GRB site is half solar, slightly below the mean metallicity at the corresponding distance from the center. Star formation in this galaxy is concentrated in a few H II regions between 5 and 7 kpc from the center and at the end of the bar, inwards from the GRB region; however the H II region hosting the GRB is in the top 10% of the regions with the highest specific star-formation rate. The stellar population at the GRB site has a very young component (&lt; 5 Myr) that contributes a significant part of the light. Ionized and molecular gas show only minor deviations at the end of the bar. A parallel study found an asymmetric H I distribution and some additional gas near the position of the GRB, which might explain the star-forming region of the GRB site. Our study shows that long GRBs can occur in many types of star-forming galaxies; however the actual GRB sites have consistently low metallicity, high star formation rates, and a young population. Furthermore, gas inflow or interactions triggering the star formation producing the GRB progenitor might not be evident in ionized or even molecular gas but only in H I.

MICONIC: JWST/MIRI MRS observations of the nuclear and circumnuclear regions of Mrk 231

We present JWST/MIRI MRS spatially resolved ∼5 − 28 μm observations of the central ∼4 − 8 kpc of the ultraluminous infrared galaxy and broad absorption line quasar Mrk 231. These are part of the Mid-Infrared Characterization of Nearby Iconic galaxy Centers (MICONIC) program of the MIRI European Consortium guaranteed time observations. No high excitation lines (i.e., [Mg V] at 5.61 μm or [Ne V] at 14.32 μm) typically associated with the presence of an active galactic nucleus (AGN) are detected in the nuclear region of Mrk 231. This is likely due to the intrinsically X-ray weak nature of its quasar. Some intermediate ionization potential lines, for instance, [Ar III] at 8.99 μm and [S IV] at 10.51 μm, are not detected either, even though they are clearly observed in a star-forming region ∼920 pc south-east of the AGN. Thus, the strong nuclear mid-infrared (mid-IR) continuum is also in part hampering the detection of faint lines in the nuclear region. The nuclear [Ne III]/[Ne II] line ratio is consistent with values observed in star-forming galaxies. Moreover, we resolve for the first time the nuclear starburst in the mid-IR low-excitation line emission (size of ∼400 pc, FWHM). Several pieces of evidence also indicate that it is partly obscured even at these wavelengths. At the AGN position, the ionized and warm molecular gas emission lines have modest widths (W80 ∼ 300 km s−1). There are, however, weak blueshifted wings reaching velocities v02 ≃ − 400 km s−1 in [Ne II]. The nuclear starburst is at the center of a large (∼8 kpc), massive rotating disk with widely-spread, low velocity outflows. Given the high star formation rate of Mrk 231, we speculate that part of the nuclear outflows and the large-scale non-circular motions observed in the mid-IR are driven by its powerful nuclear starburst.

Measuring 60 pc-scale Star Formation Rate of the Nearby Seyfert Galaxy NGC 1068 with ALMA, HST, VLT/MUSE, and VLA

The star formation rate (SFR) is a fundamental parameter for describing galaxies and inferring their evolutionary course. H ii regions yield the best measure of instantaneous SFR in galaxies, although the derived SFR can have large uncertainties depending on tracers and assumptions. We present an SFR calibration for the entire molecular gas disk of the nearby Seyfert galaxy NGC 1068, based on our new high-sensitivity Atacama Large Millimeter/submillimeter Array 100 GHz continuum data at 55 pc (= 0.″8) resolution in combination with the Hubble Space Telescope Paα line data. In this calibration, we account for the spatial variations of dust extinction, electron temperature of H ii regions, AGN contamination, and diffuse ionized gas (DIG) based on publicly available multiwavelength data. Especially, given the extended nature and the possible nonnegligible contribution to the total SFR, a careful consideration of DIG is essential. With a cross-calibration between two corrected ionized gas tracers (free–free continuum and Paα), the total SFR of the NGC 1068 disk is estimated to be 3.2 ± 0.5 M ⊙ yr−1, one-third of the SFR without accounting for DIG (9.1 ± 1.4 M ⊙ yr−1). We confirmed a high SFR around the southern bar end and the corotation radius, which is consistent with the previous SFR measurements. In addition, our total SFR exceeds the total SFR based on 8 μm dust emission by a factor of 1.5. We attribute this discrepancy to the differences in the young stars at different stages of evolution traced by each tracer and their respective timescales. This study provides an example to address the various uncertainties in conventional SFR measurements and their potential to lead to significant SFR miscalculations.

Inefficient star formation in high Mach number environments

Context. The star formation rate (SFR), the number of stars formed per unit of time, is a fundamental quantity in the evolution of the Universe. Aims. While turbulence is believed to play a crucial role in setting the SFR, the exact mechanism remains unclear. Turbulence promotes star formation by compressing the gas, but also slows it down by stabilizing the gas against gravity. Most widely used analytical models rely on questionable assumptions, including: i) integrating over the density PDF, a one-point statistical description that ignores spatial correlation, ii) selecting self-gravitating gas based on a density threshold that often ignores turbulent dispersion, iii) assuming the freefall time as the timescale for estimating SFR without considering the need to rejuvenate the density PDF, iv) assuming the density probability distribution function (PDF) to be log-normal. This leads to the reliance on fudge factors for rough agreement with simulations. Even more seriously, when a more accurate density PDF is being used, the classical theory predicts a SFR that is essentially 0. Methods. Improving upon the only existing model that incorporates the spatial correlation of the density field, we present a new analytical model that, in a companion paper, is rigorously compared against a large series of numerical simulations. We calculate the time needed to rejuvenate density fluctuations of a given density and spatial scale, revealing that it is generally much longer than the freefall time, rendering the latter inappropriate for use. Results. We make specific predictions regarding the role of the Mach number, ℳ, and the driving scale of turbulence divided by the mean Jeans length. At low to moderate Mach numbers, turbulence does not reduce and may even slightly promote star formation by broadening the PDF. However, at higher Mach numbers, most density fluctuations are stabilized by turbulent dispersion, leading to a steep drop in the SFR as the Mach number increases. A fundamental parameter is the exponent of the power spectrum of the natural logarithm of the density, ln ρ, characterizing the spatial distribution of the density field. In the high Mach regime, the SFR strongly depends on it, as lower values imply a paucity of massive, gravitationally unstable clumps. Conclusions. We provide a revised analytical model to calculate the SFR of a system, considering not only the mean density and Mach number but also the spatial distribution of the gas through the power spectrum of ln ρ, as well as the injection scale of turbulence. At low Mach numbers, the model predicts a relatively high SFR nearly independent of ℳ, whereas for high Mach, the SFR is a steeply decreasing function of ℳ.

Dwarf galaxies as a probe of a primordially magnetized Universe

Aims. The true nature of primordial magnetic fields (PMFs) and their role in the formation of galaxies remains elusive. To shed light on these unknowns, we investigated their impact by varying two sets of properties: (i) accounting for the effect of PMFs on the initial matter power spectrum and (ii) accounting for their magneto-hydrodynamical effects on the formation of galaxies. By comparing both, we can determine the dominant agent in shaping galaxy evolution. Methods. We used the magneto-hydrodynamics code RAMSES to generate multiple new zoom-in simulations for eight different host halos of dwarf galaxies across a wide luminosity range of 103 − 106 L⊙. These halos were selected from a ΛCDM cosmological box, tracking their evolution down to redshift z = 0. We explored a variety of primordial magnetic field (comoving) strengths of Bλ ranging from 0.05 to 0.50 nG. Results. We find that magnetic fields in the interstellar medium not only modify star formation processes in dwarf spheroidal galaxies, but these fields also entirely prevent the formation of stars in less compact, ultra-faint galaxies with halo masses and stellar masses below, respectively, ∼2.5 × 109 and 3 × 106 M⊙. At high redshifts, the impact of PMFs on host halos of dwarf galaxies through the modification of the matter power spectrum is more dominant than the influence of magneto-hydrodynamics in shaping their gaseous structure. Through the amplification of small perturbations ranging in mass from 107 to 109 M⊙ in the ΛCDM+PMFs matter power spectrum, primordial fields expedite the formation of the first dark matter halos, leading to an earlier onset and a higher star formation rate at redshifts of z &gt; 9. We investigated the evolution of various energy components and demonstrated that magnetic fields with an initial strength of Bλ ≥ 0.05 nG exhibit a strong growth of magnetic energy, accompanied by a saturation phase that begins soon after the growth phase. These trends persist consistently, regardless of the initial conditions or whether it is the classical ΛCDM model or ΛCDM modified by PMFs. Lastly, we investigated the impact of PMFs on the present-time observable properties of dwarf galaxies, namely: the half light radius, V-band luminosity, mean metallicity, and velocity dispersion profile. We find that PMFs with moderate strengths of Bλ ≤ 0.10 nG show an impressive agreement with the scaling relations of the observed Local Group dwarfs. However, stronger fields lead to larger sizes and higher velocity dispersions.

JWST MIRI Detections of Hα and [O iii] and a Direct Metallicity Measurement of the z = 10.17 Lensed Galaxy MACS0647−JD

JWST spectroscopy has revolutionized our understanding of galaxies in the early Universe. Covering wavelengths up to 5.3 μm, NIRSpec can detect rest-frame optical Hα emission lines out to z = 7 and [O iii] to z = 9.5. Observing these lines in more distant galaxies requires longer wavelength spectroscopy with MIRI. Here we present MIRI Medium Resolution Spectrograph integral field unit observations of the lensed galaxy merger MACS0647–JD at z = 10.165. With exposure times of 4.2 hr in each of two bands (SHORT and LONG), we detect Hα at 9σ, [O iii] λ5008 at 11σ, and [O iii] λ4960 at 3σ. Combined with previously reported NIRSpec spectroscopy that yielded seven emission lines including the auroral line [O iii] λ4363, we present the first direct metallicity measurement of a z > 10 galaxy: 12+log(O/H)=7.79±0.09 , or 0.13−0.03+0.02Z⊙ . This is similar to galaxies at z ∼ 4–9 with direct metallicity measurements, though higher than expected given the high specific star formation rate log(sSFR/yr−1) = −7.4 ± 0.3. We further constrain the ionization parameter log(U) = −1.9 ± 0.1, ionizing photon production efficiency log(ξ ion) = 25.3 ± 0.1, and SFR = 5.0 ± 0.6 M ⊙ yr−1 within the past 10 Myr. These observations demonstrate the combined power of JWST NIRSpec and MIRI for studying galaxies in the first 500 million years.

Searching for pulsars, magnetars, and fast radio bursts in the sculptor galaxy using MeerKAT

Abstract The Sculptor Galaxy (NGC 253), located in the Southern Hemisphere, far off the Galactic Plane, has a relatively high star-formation rate of about 7 M⊙ yr−1 and hosts a young and bright stellar population, including several super star clusters and supernova remnants. It is also the first galaxy, apart from the Milky Way Galaxy to be associated with two giant magnetar flares. As such, it is a potential host of pulsars and/or fast radio bursts in the nearby Universe. The instantaneous sensitivity and multibeam sky coverage offered by MeerKAT therefore make it a favourable target. We searched for pulsars, radio-emitting magnetars, and fast radio bursts in NGC 253 as part of the TRAPUM large survey project with MeerKAT. We did not find any pulsars during a four-hour observation, and derive a flux density limit of 4.4 μJy at 1400 MHz, limiting the pseudo-luminosity of the brightest putative pulsar in this galaxy to 54 Jy kpc2. Assuming universality of pulsar populations between galaxies, we estimate that detecting a pulsar as bright as this limit requires NGC 253 to contain a pulsar population of ⪞20 000. We also did not detect any single pulses and our single pulse search flux density limit is 62 mJy at 1284 MHz. Our search is sensitive enough to have detected any fast radio bursts and radio emission similar to the brighter pulses seen from the magnetar SGR J1935+2154 if they had occurred during our observation.