arXiv subjects

Kentaro Motohara

Publications and source records attributed to Kentaro Motohara.

At least 19 recordsLinked to original sources

arXiv2026

MORFEO: Advancing Towards Final Design

The Multiconjugate adaptive Optics Relay For ELT Observations (MORFEO) is a first-generation adaptive optics module for the Extremely Large Telescope (ELT), designed to deliver a diffraction-limited, highly uniform 53x53 arcsec field of view to the MICADO near-infrared camera. As the project advances toward its Final Design Review (FDR), significant consolidations have been achieved across all subsystems. This paper presents an updated overview of the MORFEO system, highlighting its dual operational modes (MCAO and SCAO) and recent developments in its opto-mechanical architecture. We dedicate specific focus to the core adaptive hardware, detailing the fifth-generation post-focal deformable mirrors, the highly complex Laser Guide Star (LGS) objective zoom system required to track sodium layer variations, and the Natural Guide Star (NGS) low-order and reference sensing strategies. Furthermore, we detail the advanced pseudo-open-loop control strategy managed by a split Hard and Soft Real-Time Computer architecture. Finally, we report the latest end-to-end performance estimations obtained via the SPECULA simulation framework, demonstrating compliance with the stringent Strehl Ratio and sky coverage requirements under median atmospheric conditions.

astro-ph.IM↗

arXiv2025

Association of cold gas, massive galaxies, and AGNs in a filamentary protocluster traced by triple narrow-band imaging

We investigate galaxy populations in the HS1700+64 protocluster at $z=2.30$, characterized by two prominent linear filaments traced by spatially extended Ly$\alpha$ blobs. We conducted a wide area mapping of emission line galaxies across the protocluster using the unique combination of three matched narrow-band filters, corresponding to Ly$\alpha$, H$\alpha$, and [OIII] emission lines at $z=2.30$. We find that H$\alpha$ emitters are strongly clustered at the intersection of the filaments, suggesting a protocluster core. In contrast, Ly$\alpha$ emitters tend to avoid the dense region and the filaments, likely due to the resonant scattering of Ly$\alpha$ photons by HII gas and/or enhanced dust attenuation in galaxies associated with these structures. These findings support a scenario in which cold gas flows via filaments and to the core, fed by the cold-stream mode accretion in the early phase of protocluster assembly, and promoting active star formation there. Further evidence of the scenario comes from the alignment of massive, evolved galaxies in those filaments traced by distant red galaxies, suggesting accelerated galaxy growth in the filaments in the early Universe. This study clearly shows observationally that accelerated galaxy formation takes place not only in the protocluster core but also in the associated surrounding filamentary structure. This underscores the critical role of large-scale filaments in efficiently accumulating the cold gas and channeling it to galaxies therein and to the protocluster core. Such vigorous gas assembly facilitates star formation activity and drives galaxy growth in the early stage of cluster formation.

astro-ph.GA↗

arXiv2025

Environmental Regulation of Dust and Star Formation Unveiled by Subaru Dual Narrow-band Imaging: Degree-scale Balmer Decrement Mapping across a z = 0.9 Supercluster

We present results from a dual narrow-band imaging survey targeting the CL1604 supercluster at z = 0.9 using the Subaru Telescope. By combining the NB921 filter on HSC and the NB1244 filter on SWIMS, we can detect redshifted H$\alpha$ and H$\beta$ emission lines from the supercluster. This unique technique allows us to measure both star formation rates and dust extinction for a sample of 94 emission-line galaxies across the supercluster. We find that dust extinction, estimated from the Balmer decrement (H$\alpha$/H$\beta$ ratio), increases with stellar mass in star-forming galaxies, whereas relatively quiescent systems exhibit comparatively low extinction. Among galaxies with intermediate masses ($10^{8.5} < M_* < 10^{10.5}\,M_\odot$), the dust-corrected H$\alpha$-based star formation rates align with the main sequence at this epoch. More massive galaxies, however, deviate from this relation, exhibit redder colors, and reside predominantly in higher-density environments. Although stellar mass, SFR, and galaxy color are clearly influenced by environment, we detect no strong, systematic environmental dependence of dust extinction for the whole sample.

astro-ph.GA↗

arXiv2025

Early-type Galaxies on the Star Formation Main Sequence: Internal Star Formation Geometry Revealed with MaNGA and Their Environmental Origin

Star-forming galaxies on the main sequence (MS) are often regarded as a uniform population characterized by similar global star formation properties. However, there exists a diversity in galaxy morphologies at fixed stellar mass and SFR. In this study, using spatially-resolved properties from the MaNGA final data release, we classify MS galaxies into late-type (MS-late) and early-type (MS-early). In addition, we further divide the MS-early galaxies into two distinct subgroups based on their internal star formation and stellar mass distributions within the galaxies. The first group -- ``MS-early\_SF'' -- shows centrally concentrated star formation without prominent stellar bulges and resides preferentially in dense environments, suggesting environmentally-driven evolution. The second group -- ``MS-early\_stellar'' -- exhibits significant stellar bulges with suppressed central star formation, maintains disk-like star formation patterns, and inhabits environments similar to those of late-type galaxies, indicating evolution through internal secular processes. Our findings demonstrate that spatially-resolved observations play critical roles in revealing the diverse evolutionary pathways hidden within galaxies that share similar global properties.

astro-ph.GA↗

arXiv2025

A recoiling supermassive black hole in a powerful quasar

Supermassive black holes (SMBH) are thought to grow through accretion of matter and mergers. Models of SMBH mergers have long suffered the final parsec problem, where SMBH binaries may stall before energy loss from gravitational waves (GW) becomes significant, leaving the pair unmerged. Direct evidence of coalesced SMBH remains elusive. Theory predicts that GW recoiling black holes can occur following a black hole merger. Here we present new and conclusive spectroscopic evidence that both the accretion disk and the broad line region in the spatially offset quasar 3C 186 are blue-shifted by the same velocity relative to the host galaxy, with a line of sight velocity of (-1310 +- 21) km/s. This is best explained by the GW recoil super-kick scenario. This confirmation of the ejection process implies that the final parsec problem is resolved in nature, providing evidence that even the most massive black holes can merge.

astro-ph.GA↗

arXiv2024

EMPRESS. X. Spatially resolved mass-metallicity relation in extremely metal-poor galaxies: evidence of episodic star-formation fueled by a metal-poor gas infall

Using the Subaru/FOCAS IFU capability, we examine the spatially resolved relationships between gas-phase metallicity, stellar mass, and star-formation rate surface densities (Sigma_* and Sigma_SFR, respectively) in extremely metal-poor galaxies (EMPGs) in the local universe. Our analysis includes 24 EMPGs, comprising 9,177 spaxels, which span a unique parameter space of local metallicity (12+log(O/H) = 6.9 to 7.9) and stellar mass surface density (Sigma_* ~ 10^5 to 10^7 Msun/kpc^2), extending beyond the range of existing large integral-field spectroscopic surveys. Through spatially resolved emission line diagnostics based on the [NII] BPT-diagram, we verify the absence of evolved active galactic nuclei in these EMPGs. Our findings reveal that, while the resolved mass-metallicity relation exhibits significant scatter in the low-mass regime, this scatter is closely correlated with local star-formation surface density. Specifically, metallicity decreases as Sigma_SFR increases for a given Sigma_*. Notably, half of the EMPGs show a distinct metal-poor horizontal branch on the resolved mass-metallicity relation. This feature typically appears at the peak clump with the highest Sigma_* and Sigma_SFR and is surrounded by a relatively metal-enriched ambient region. These findings support a scenario in which metal-poor gas infall fuels episodic star formation in EMPGs, consistent with the kinematic properties observed in these systems. In addition, we identify four EMPGs with exceptionally low central metallicities (12+log(O/H) <~ 7.2), which display only a metal-poor clump without a surrounding metal-rich region. This suggests that such ultra-low metallicity EMPGs, at less than a few percent of the solar metallicity, may serve as valuable analogs for galaxies in the early stages of galaxy evolution.

astro-ph.GA↗

arXiv2024

Compact [OIII] emission-line regions ("Green Seeds") in $\mathrm{H\alpha}$ emitters at Cosmic Noon from JWST Observations

We present a rest-frame optical, spatially resolved analysis of more than 100 $\mathrm{H\alpha}$ emitters (HAEs) at $z\sim2.2$ in the ZFOURGE-CDFS field using NIRCam imaging from the JWST Advanced Deep Extragalactic Survey (JADES). The ultra-deep, high-resolution data gives us maps of the resolved emission line regions of HAEs with stellar mass ranging from $10^{8}\,M_{\odot}$ to $10^{10}\,M_{\odot}$. An [OIII] emission-line map of each HAE is created from the flux excess in the F150W filter, leading to the discovery of a population of kiloparsec-scale compact emission line regions (``Green Seeds") with high equivalent widths ($\mathrm{EW}$). We obtain a sample of 128 Green Seeds from 68 HAEs with rest-frame $\mathrm{EW_{[OIII]}}>200\r{A}$. Moreover, 17 of them have extremely large $\mathrm{EW_{[OIII]}}>1000\r{A}$, suggesting the possible Lyman continuum (LyC) leakage from these emission line regions. Embedded within the host galaxy, many Green Seeds correspond to UV star-forming clumps and H{\sc ii} regions, indicating elevated starburst activity in them, with specific star formation rates (sSFR) several times higher than that of the host galaxy. Based on theoretical frameworks, Green Seeds are expected to be formed through gravitational disk instability and/or galaxy mergers. Considering the stellar masses of Green Seeds, we speculate that high-mass Green Seeds may migrate toward the galactic center to build the central bulge, while low-mass Green Seeds are easily disrupted and short-lived. Besides, we propose that some Green Seeds could be the progenitors of globular clusters or ultracompact dwarf galaxies observed in the local universe.

astro-ph.GA↗

arXiv2024

Report of the Kavli-IAU Workshop on Global Coordination, "Probing the Universe from far-infrared to millimeter wavelengths: future facilities and their synergies"

This Report summarizes findings and recommendations from the Kavli-IAU workshop on "Probing the Universe from far-infrared to millimeter wavelengths: future facilities and their synergies" which took place from 26 to 28 March 2024 in Pasadena, CA, USA. The workshop aimed to define the needs and potential synergies for different facilities at wavelengths from 30 μm to a few cm in the post-2030 era, considering both financial and programmatic limitations and exploring how to maximize the scientific insights from the data they will yield in the coming decades. This wavelength range provides unique probes of relatively cool, dense interstellar material central to studying the physics and chemistry of nascent stars, proton-planetary disks, and young forming exoplanets. On larger scales, these facilities probe dust and dense gas in galaxies and around highly obscured accreting supermassive black holes and are thus essential for characterizing feedback processes and galaxy evolution out to the highest redshifts. Solar system and time domain studies are also addressed. The main recommendations include the need for ALMA to develop an ALMA2040 vision; for ngVLA to maintain its momentum and schedule and further develop international partnerships; for far-IR astronomy to pursue a space-based observatory with urgency; and for large aperture, wide field millimeter/submillimeter telescopes to continue studies to mature science and technology.

astro-ph.IM↗

arXiv2024

Towards unveiling the Cosmic Reionization: the ionizing photon production efficiency ($ξ_{ion}$) of Low-mass H$α$ emitters at $z \sim 2.3$

We investigate the galaxy properties of $\sim$400 low-mass ($<10^9\,M_{\odot}$) H$α$ emitters (HAEs) at z $\sim$ 2.3 in the ZFOURGE survey. The selection of these HAEs is based on the excess in the observed $K_s$ broad-band flux compared to the stellar continuum estimated from the best-fit SED. These low-mass HAEs have elevated SFR(H$α$) above the star formation main sequence (SFMS), making them potential analogs of the galaxies that reionized the universe during the epoch of reionization. The ionizing photon production efficiencies ($ξ_{ion}$) of the low-mass HAEs have a median value of $\mathrm{log}(ξ_{ion}/erg^{-1} Hz)=25.24^{+0.10}_{-0.13}\ (25.35^{+0.12}_{-0.15})$, assuming the Calzetti (SMC) curve for the stellar continuum dust correction. This value is higher than that of main sequence galaxies by $\sim$0.2 dex at similar redshift, indicating that the low-mass HAEs are more efficient in producing ionizing photons. Our results also consolidate the trend of increasing $ξ_{ion}$ with redshift, but reveal a "downsizing" relationship between $ξ_{ion}$ and stellar mass ($M_{\odot}$) with increasing redshift. We further explore the dependence of $ξ_{ion}$ on other galaxy properties, such as the UV spectral slope ($β_{\mathrm{UV}}$), the UV magnitude ($M_{\mathrm{UV}}$), the equivalent widths ($EWs$) of H$α$ and [O{\sc iii}] emission lines. Galaxies with the bluer UV slopes, fainter UV luminosities and higher equivalent widths exhibit elevated $ξ_{ion}$ by a factor of $\sim$2 compared to the median $ξ_{ion}$ of our sample. JWST data will provide an opportunity to extend our method and further investigate the properties of low-mass galaxies at high redshifts.

astro-ph.GA↗

arXiv2024

Multiple emission lines of H$α$ emitters at $z \sim 2.3$ from the broad and medium-band photometry in the ZFOURGE Survey

We present a multiple emission lines study of $\sim$1300 H$α$ emitters (HAEs) at $z \sim 2.3$ in the ZFOURGE survey. In contrast to the traditional spectroscopic method, our sample is selected based on the flux excess in the ZFOURGE-$K_s$ broad-band data relative to the best-fit stellar continuum. Using the same method, we also extract the strong diagnostic emission lines for these individual HAEs: [OIII]$λ\lambda4959,5007$, [OII]$λ\lambda3726,3729$. Our measurements exhibit good consistency with those obtained from spectroscopic surveys. We investigate the relationship between the equivalent widths (EWs) of these emission lines and various galaxy properties, including stellar mass, stellar age, star formation rate (SFR), specific SFR (sSFR), ionization states (O32). We have identified a discrepancy between between HAEs at $z\sim2.3$ and typical local star-forming galaxy observed in the SDSS, suggesting the evolution of lower gas-phase metallicity ($Z$) and higher ionization parameters ($U$) with redshift. Notably, we have observed a significant number of low-mass HAEs exhibiting exceptionally high $EW_{\mathrm{[OIII]}}$. Their galaxy properties are comparable to those of extreme objects, such as extreme O3 emitters (O3Es) and Ly$α$ emitters (LAEs) at $z\simeq2-3$. Considering that these characteristics may indicate potential strong Lyman continuum (LyC) leakage, higher redshift anaglogs of the low-mass HAEs could be significant contributors to the cosmic reionization. Further investigations on this particular population are required to gain a clearer understanding of galaxy evolution and cosmic reionization.

astro-ph.GA↗

arXiv2024

Development of a near-infrared wide-field integral field unit by ultra-precision diamond cutting

Integral Field Spectroscopy (IFS) is an observational method to obtain spatially resolved spectra over a specific field of view (FoV) in a single exposure. In recent years, near-infrared IFS has gained importance in observing objects with strong dust attenuation or at high redshift. One limitation of existing near-infrared IFS instruments is their relatively small FoV, less than 100 arcsec$^2$, compared to optical instruments. Therefore, we have developed a near-infrared (0.9-2.5 $\mathrmμ$m) image-slicer type integral field unit (IFU) with a larger FoV of 13.5 $\times$ 10.4 arcsec$^2$ by matching a slice width to a typical seeing size of 0.4 arcsec. The IFU has a compact optical design utilizing off-axis ellipsoidal mirrors to reduce aberrations. Complex optical elements were fabricated using an ultra-precision cutting machine to achieve RMS surface roughness of less than 10 nm and a P-V shape error of less than 300 nm. The ultra-precision machining can also simplify alignment procedures. The on-sky performance evaluation confirmed that the image quality and the throughput of the IFU were as designed. In conclusion, we have successfully developed a compact IFU utilizing an ultra-precision cutting technique, almost fulfilling the requirements.

astro-ph.IM↗

arXiv2024

EMPRESS. XII. Statistics on the Dynamics and Gas Mass Fraction of Extremely-Metal Poor Galaxies

We present demography of the dynamics and gas-mass fraction of 33 extremely metal-poor galaxies (EMPGs) with metallicities of $0.015-0.195~Z_\odot$ and low stellar masses of $10^4-10^8~M_\odot$ in the local universe. We conduct deep optical integral-field spectroscopy (IFS) for the low-mass EMPGs with the medium high resolution ($R=7500$) grism of the 8m-Subaru FOCAS IFU instrument by the EMPRESS 3D survey, and investigate H$α$ emission of the EMPGs. Exploiting the resolution high enough for the low-mass galaxies, we derive gas dynamics with the H$α$ lines by the fitting of 3-dimensional disk models. We obtain an average maximum rotation velocity ($v_\mathrm{rot}$) of $15\pm3~\mathrm{km~s^{-1}}$ and an average intrinsic velocity dispersion ($σ_0$) of $27\pm10~\mathrm{km~s^{-1}}$ for 15 spatially resolved EMPGs out of the 33 EMPGs, and find that all of the 15 EMPGs have $v_\mathrm{rot}/σ_0<1$ suggesting dispersion dominated systems. There is a clear decreasing trend of $v_\mathrm{rot}/σ_0$ with the decreasing stellar mass and metallicity. We derive the gas mass fraction ($f_\mathrm{gas}$) for all of the 33 EMPGs, and find no clear dependence on stellar mass and metallicity. These $v_\mathrm{rot}/σ_0$ and $f_\mathrm{gas}$ trends should be compared with young high-$z$ galaxies observed by the forthcoming JWST IFS programs to understand the physical origins of the EMPGs in the local universe.

astro-ph.GA↗

arXiv2023

EMPRESS. IX. Extremely Metal-Poor Galaxies are Very Gas-Rich Dispersion-Dominated Systems: Will JWST Witness Gaseous Turbulent High-z Primordial Galaxies?

We present kinematics of 6 local extremely metal-poor galaxies (EMPGs) with low metallicities ($0.016-0.098\ Z_{\odot}$) and low stellar masses ($10^{4.7}-10^{7.6} M_{\odot}$). Taking deep medium-high resolution ($R\sim7500$) integral-field spectra with 8.2-m Subaru, we resolve the small inner velocity gradients and dispersions of the EMPGs with H$α$ emission. Carefully masking out sub-structures originated by inflow and/or outflow, we fit 3-dimensional disk models to the observed H$α$ flux, velocity, and velocity-dispersion maps. All the EMPGs show rotational velocities ($v_{\rm rot}$) of 5--23 km s$^{-1}$ smaller than the velocity dispersions ($σ_{0}$) of 17--31 km s$^{-1}$, indicating dispersion-dominated ($v_{\rm rot}/σ_{0}=0.29-0.80<1$) systems affected by inflow and/or outflow. Except for two EMPGs with large uncertainties, we find that the EMPGs have very large gas-mass fractions of $f_{\rm gas}\simeq 0.9-1.0$. Comparing our results with other H$α$ kinematics studies, we find that $v_{\rm rot}/σ_{0}$ decreases and $f_{\rm gas}$ increases with decreasing metallicity, decreasing stellar mass, and increasing specific star-formation rate. We also find that simulated high-$z$ ($z\sim 7$) forming galaxies have gas fractions and dynamics similar to the observed EMPGs. Our EMPG observations and the simulations suggest that primordial galaxies are gas-rich dispersion-dominated systems, which would be identified by the forthcoming James Webb Space Telescope (JWST) observations at $z\sim 7$.

astro-ph.GA↗

arXiv2023

The hidden side of cosmic star formation at z > 3: Bridging optically-dark and Lyman break galaxies with GOODS-ALMA

Our current understanding of the cosmic star formation history at z>3 is primarily based on UV-selected galaxies (i.e., LBGs). Recent studies of H-dropouts have revealed that we may be missing a large proportion of star formation that is taking place in massive galaxies at z>3. In this work, we extend the H-dropout criterion to lower masses to select optically dark/faint galaxies (OFGs), in order to complete the census between LBGs and H-dropouts. Our criterion (H> 26.5 mag & [4.5] < 25 mag) combined with a de-blending technique is designed to select not only extremely dust-obscured massive galaxies but also normal star-forming galaxies. In total, we identified 27 OFGs at z_phot > 3 (z_med=4.1) in the GOODS-ALMA field, covering a wide distribution of stellar masses with log($M_{\star}$/$M_{\odot}$) = 9.4-11.1. We find that up to 75% of the OFGs with log($M_{\star}$/$M_{\odot}$) = 9.5-10.5 were neglected by previous LBGs and H-dropout selection techniques. After performing stacking analyses, the OFGs exhibit shorter gas depletion timescales, slightly lower gas fractions, and lower dust temperatures than typical star-forming galaxies. Their SFR_tot (SFR_ IR+SFR_UV) is much larger than SFR_UVcorr (corrected for dust extinction), with SFR_tot/SFR_UVcorr = $8\pm1$, suggesting the presence of hidden dust regions in the OFGs that absorb all UV photons. The average dust size measured by a circular Gaussian model fit is R_e(1.13 mm)=1.01$\pm$0.05 kpc. We find that the cosmic SFRD at z>3 contributed by massive OFGs is at least two orders of magnitude higher than the one contributed by equivalently massive LBGs. Finally, we calculate the combined contribution of OFGs and LBGs to the cosmic SFRD at z=4-5 to be 4 $\times$ 10$^{-2}$ $M_{\odot}$ yr$^{-1}$Mpc$^{-3}$, which is about 0.15 dex (43%) higher than the SFRD derived from UV-selected samples alone at the same redshift.

astro-ph.GA↗

arXiv2023

SN 2020uem: A Possible Thermonuclear Explosion within A Dense Circumstellar Medium (I) The Nature of Type IIn/Ia-CSM SNe from Photometry and Spectroscopy

We have performed intensive follow-up observations of a Type IIn/Ia-CSM SN (SN IIn/Ia-CSM), 2020uem, with photometry, spectroscopy, and polarimetry. In this paper, we report on the results of our observations focusing on optical/near-infrared (NIR) photometry and spectroscopy. The maximum V-band magnitude of SN 2020uem is over $-19.5$ mag. The light curves decline slowly with a rate of $\sim 0.75 {\rm ~mag}/100 {\rm ~days}$. In the late phase ($\gtrsim 300$ days), the light curves show accelerated decay ($\sim 1.2 {\rm ~mag}/100 {\rm ~days}$). The optical spectra show prominent hydrogen emission lines and broad features possibly associated with Fe-peak elements. In addition, the $\rm Hα$ profile exhibits a narrow P-Cygni profile with the absorption minimum of $\sim 100 {\rm ~km~s^{-1}}$. SN 2020uem shows a higher $\rm Hα/Hβ$ ratio ($\sim 7$) than those of SNe IIn, which suggests a denser CSM. The NIR spectrum shows the Paschen and Brackett series with continuum excess in the H and Ks bands. We conclude that the NIR excess emission originates from newly-formed carbon dust. The dust mass ($M_{\rm d}$) and temperature ($T_{\rm d}$) are derived to be $(M_{\rm d}, T_{\rm d}) \sim (4-7 \times 10^{-5} {\rm ~M_{\odot}}, 1500-1600 {\rm ~K})$. We discuss the differences and similarities between the observational properties of SNe IIn/Ia-CSM and those of other SNe Ia and interacting SNe. In particular, spectral features around $\sim 4650$ {\text Å} and $\sim 5900$ {\text Å} of SNe IIn/Ia-CSM are more suppressed than those of SNe Ia; these lines are possibly contributed, at least partly, by \ion{Mg}{1}] and \ion{Na}{1}, and may be suppressed by high ionization behind the reverse shock caused by the massive CSM.

astro-ph.HE↗

arXiv2023

A selection of Hα emitters at z = 2.1-2.5 using the Ks-band photometry of ZFOURGE

Large and less-biased samples of star-forming galaxies are essential to investigate galaxy evolution. H$\rmα$ emission line is one of the most reliable tracers of star-forming galaxies because its strength is directly related to recent star formation. However, it is observationally expensive to construct large samples of H$\rmα$ emitters by spectroscopic or narrow-band imaging survey at high-redshifts. In this work, we demonstrate a method to extract H$\rmα$ fluxes of galaxies at $z=2.1$-$2.5$ from $K_s$ broad-band photometry of ZFOURGE catalog. Combined with 25-39 other filters, we estimate the emission line fluxes by SED fitting with stellar population models that incorporate emission-line strengths. 2005 galaxies are selected as H$\rmα$ emitters by our method and their fluxes show good agreement with previous measurements in the literature. On the other hand, there are more H$\rmα$ luminous galaxies than previously reported. The discrepancy can be explained by extended H$\rmα$ profiles of massive galaxies and a luminosity dependence of dust attenuation, which are not taken into account in the previous work. We also find that there are a large number of low-mass galaxies with much higher specific star formation rate (sSFR) than expected from the extrapolated star formation main sequence. Such low-mass galaxies exhibit larger ratios between H$\rmα$ and UV fluxes compared to more massive high sSFR galaxies. This result implies that a ``starburst'' mode may differ among galaxies: low-mass galaxies appear to assemble their stellar mass via short-duration bursts while more massive galaxies tend to experience longer-duration ($>10\ \mathrm{Myr}$) bursts.

astro-ph.GA↗

arXiv2022

EMPRESS. VIII. A New Determination of Primordial He Abundance with Extremely Metal-Poor Galaxies: A Suggestion of the Lepton Asymmetry and Implications for the Hubble Tension

The primordial He abundance $Y_\mathrm{P}$ is a powerful probe of cosmology. Currently, $Y_\mathrm{P}$ is best determined by observations of metal-poor galaxies, while there are only a few known local extremely metal-poor ($<0.1 Z_\odot$) galaxies (EMPGs) having reliable He/H measurements with HeI$λ$10830 near-infrared (NIR) emission. Here we present deep Subaru NIR spectroscopy for 10 EMPGs. Combining the existing optical data, He/H values of 5 out of the 10 EMPGs are reliably derived by the Markov chain Monte Carlo algorithm. Adding the existing 3 EMPGs and 51 moderately metal-poor ($0.1-0.4 Z_\odot$) galaxies with reliable He/H estimates, we obtain $Y_\mathrm{P}=0.2370^{+0.0034}_{-0.0033}$ by linear regression in the $\mathrm{(He/H)}-\mathrm{(O/H)}$ plane, where we increase the number of EMPGs from 3 to 8 anchoring He/H of the most metal-poor gas in galaxies. Although our $Y_\mathrm{P}$ measurement and previous measurements are consistent, our result is slightly ($\sim 1σ$) smaller due to our EMPGs. With our $Y_\mathrm{P}$ and the existing primordial deuterium $D_\mathrm{P}$ measurement, we constrain the effective number of neutrino species $N_\mathrm{eff}$ and the baryon-to-photon ratio $η$ showing $\gtrsim 1-2σ$ tensions with the Standard Model and Planck Collaboration et al. (2020). Motivated by the tensions, we allow the degeneracy parameter of electron-neutrino $ξ_e$ to vary as well as $N_\mathrm{eff}$ and $η$. We obtain $ξ_e = 0.05^{+0.03}_{-0.02}$, $N_\mathrm{eff}=3.11^{+0.34}_{-0.31}$, and $η\times10^{10}=6.08^{+0.06}_{-0.06}$ from the $Y_\mathrm{P}$ and $D_\mathrm{P}$ measurements with a prior of $η$ taken from Planck Collaboration et al. (2020). Our constraints suggest a lepton asymmetry and allow for a high value of $N_\mathrm{eff}$ within the $1σ$ level, which could mitigate the Hubble tension.

astro-ph.CO↗

arXiv2022

Multi-wavelength and Multi-CO View of The Minor Merger Driven Star Formation in the Nearby LIRG NGC 3110

We present Atacama Large Millimeter/submillimeter Array observations of multiple CO(1-0), $^{13}$CO(1-0), and C$^{18}$O(1-0) lines and 2.9 mm and 1.3 mm continuum emission toward the nearby interacting luminous infrared galaxy NGC 3110, supplemented with similar spatial resolution H$α$, 1.4GHz continuum, and $K$-band data. We estimate the typical CO-to-H$_2$ conversion factor of 1.7 $M_{\odot}$ (K km s$^{-1}$ pc$^2$)$^{-1}$ within the disk using LTE-based and dust-based H$_2$ column densities, and measure the 1-kpc scale surface densities of star formation rate ($Σ_{\rm SFR}$), super star clusters ($Σ_{\rm SSC}$), molecular gas mass, and star formation efficiency (SFE) toward the entire gas disk. These parameters show a peak at the southern part of the southern spiral arm (SFE $\sim$ 10$^{-8.2}$ yr$^{-1}$, $Σ_{\rm SFR}$ $\sim$ 10$^{-0.6}$ $M_{\odot}$ kpc$^{-2}$ yr$^{-1}$, $Σ_{\rm SSC}$ $\sim$ 6.0 kpc$^{-2}$), which is likely attributed to the on-going tidal interaction with the companion galaxy MCG-01-26-013, as well as toward the circumnuclear region. We also find that thermal free-free emission contributes to a significant fraction of the millimeter continuum emission at the southern peak position. Those measurements imply that the peak of the southern arm is an active and young star-forming region, whereas the central part of NGC 3110 is a site of long-continued star formation. We suggest that, during the early stage of the galaxy-galaxy interaction with large mass ratio that in NGC 3110, fragmentation along the main galaxy's arms is an important driver of merger-induced star formation and massive gas inflow results in dusty nuclear starbursts.

astro-ph.GA↗