Large Equivalent Width Research Articles

An Intermediate-mass Black Hole Hidden behind Thick Obscuration

Recent models suggest approximately half of all accreting supermassive black holes (SMBHs; M BH ≳ 105 M ⊙) are expected to undergo intense growth phases behind Compton-thick (N H > 1.5 × 1024 cm−2) veils of obscuring gas. However, despite being a viable source for the seeding of SMBHs, there are currently no examples known of a Compton-thick accreting intermediate-mass black hole (IMBH; M BH ∼ 102–105 M ⊙). We present a detailed X-ray spectral analysis of IC 750—the only active galactic nuclei (AGN) to date with a precise megamaser-based intermediate mass <105 M ⊙. We find the equivalent width of neutral 6.4 keV Fe Kα to be 1.9−1.0+2.2 keV via phenomenological modeling of the coadded 177 ks Chandra spectrum. Such large equivalent widths are seldom produced by processes other than fluorescence from dense obscuration. We fit three physically motivated X-ray spectral models to infer a range of possible intrinsic 2–10 keV luminosity posteriors that encompass the systematic uncertainties associated with a choice of model. Despite a wide range of predicted intrinsic 2–10 keV luminosities between ∼ 1041 and 1043 erg s−1, all three models agree that IC 750 has a Compton-thick line-of-sight column density to >99% confidence. Compton-thick obscuration is well-documented to impinge substantial bias on the pursuit of SMBH AGN. Our results thus provide the first indication that Compton-thick obscuration should also be properly considered to uncover and understand the IMBH population in an unbiased manner.

JWST/NIRSpec Observations of Lyman α Emission in Star-forming Galaxies at 6.5 ≲ z ≲ 13

We present an analysis of JWST Lyα spectroscopy of z ≳ 6.5 galaxies, using observations in the public archive covering galaxies in four independent fields: Great Observatories Origins Deep Survey (GOODS)-N, GOODS-S, A2744, and the Extended Groth Strip (EGS). We measure the Lyα emission line properties for a sample of 210 z ≃ 6.5–13 galaxies, with redshifts confirmed independently of Lyα in all cases. We present three new detections of Lyα emission in JWST spectra, including a large equivalent width (EW; =143 Å) Lyα emitter (LAE) with strong C iv emission (EW = 21 Å) at z = 7.1 in GOODS-N. We measure the redshift-dependent Lyα EW distribution across our sample. We find that strong Lyα emission (EW > 25 Å) becomes increasingly rare at earlier epochs, suggesting that the transmission of Lyα photons decreases by 4× between z ≃ 5 and z ≃ 9. We describe potential implications for the intergalactic medium neutral fraction. There is significant field-to-field variance in the LAE fraction. In contrast to the three other fields, the EGS shows no evidence for reduced transmission of Lyα photons at z ≃ 7–8, suggesting a significantly ionized sight line may be present in the field. We use available NIRCam grism observations from the First Reionization Epoch Spectroscopically Complete Observations survey to characterize overdensities on large scales around known LAEs in the GOODS fields. The strongest overdensities appear linked with extremely strong Lyα detections (EW > 50 Å) in most cases. Future Lyα spectroscopy with JWST has the potential to constrain the size of ionized regions around early galaxy overdensities, providing a new probe of the reionization process.

Extreme emission line galaxies detected in JADES JWST/NIRSpec – I. Inferred galaxy properties

ABSTRACT Extreme emission line galaxies (EELGs) exhibit large equivalent widths (EW) in their rest-optical emission lines ([O iii]$\lambda 5007$ or H $\alpha$ rest-frame EW$\gt 750$ Å) which can be tied to a recent upturn in star formation rate (SFR), due to the sensitivity of the nebular line emission and the rest-optical continuum to young ($\lt 10$ Myr) and evolved stellar populations, respectively. By studying a sample of 85 star-forming galaxies (SFGs), spanning the redshift and magnitude interval $3 \lt z\lt 9.5$ and $-16\gt $M$\rm _{UV}\gt -21$, in the JWST Advanced Deep Extragalactic Survey (JADES) with NIRSpec/prism spectroscopy, we determine that SFGs initiate an EELG phase when entering a significant burst of star formation, with the highest EWs observed in EELGs with the youngest luminosity-weighted ages ($\lt 5$ Myr) and the highest burst intensity (those with the greatest excess between their current and long-term average SFR). We spectroscopically confirm that a greater proportion of SFGs are in an EELG phase at high redshift in our UV-selected sample ($61\pm 4~{{\ \rm per\ cent}}$ in our $z\gt 5.7$ high-redshift bin, compared to $23^{+4}_{-1}\%$ in our lowest redshift bin $3\lt z\lt 4.1$) due to the combined evolution of metallicity, ionization parameter, and star formation histories with redshift. We report that the EELGs within our sample exhibit a higher average ionization efficiency ($\log _{10}(\xi _\mathrm{ion}^\mathrm{HII}/{\rm erg^{-1}Hz}) =25.5\pm 0.2$) than the non-EELGs. High-redshift EELGs therefore comprise a population of efficient ionizing photon producers. Additionally, we report that 53 per cent (9/17) of EELGs at $z\gt 5.7$ have observed Ly $\alpha$ emission, potentially lying within large ionized regions. The high detection rate of Ly $\alpha$ emitters in our EELG selection suggests that the physical conditions associated with entering an EELG phase also promote the escape of Ly $\alpha$ photons.

JWST spectroscopy of z ∼ 5–8 UV-selected galaxies: new constraints on the evolution of the Ly α escape fraction in the reionization era

ABSTRACT We describe JWST/NIRSpec prism measurements of Ly α emission in z ≳ 5 galaxies. We identify Ly α detections in 10 out of 69 galaxies with robust rest-optical emission-line redshift measurements at 5 ≤ z &amp;lt; 7 in the Cosmic Evolution Early Release Science (CEERS) and DDT-2750 observations of the Extended Groth Strip field. Galaxies at z ≃ 6 with faint continuum (F150W=27–29 mag) are found with extremely large rest-frame Ly α equivalent widths (EWs; ranging up to 286 Å). Likely Ly α detections are also seen in two new z &amp;gt; 7 galaxies (z = 7.49 and 7.17) from the second epoch of CEERS observations, both showing large Ly α EWs that likely indicate significant transmission through the intergalactic medium (IGM). We measure high Ly α escape fractions in the 12 Ly α emitters in our sample (median 0.28), two of which show $f_{\rm esc}^{ {\rm Ly}\alpha }$ near unity (&amp;gt;0.80). We find that $50_{-11}^{+11}$ per cent of z ≃ 6 galaxies with [O iii] + H β EW&amp;gt;1000 Å have $f_{\rm esc}^{ {\rm Ly}\alpha }$ &amp;gt;0.2, consistent with the fractions found in lower redshift samples with matched [O iii] + H β EWs. While uncertainties are still significant, we find that only $10_{-5}^{+9}$ per cent of z &amp;gt; 7 galaxies with similarly strong rest optical emission lines show such large $f_{\rm esc}^{ {\rm Ly}\alpha }$, as may be expected if IGM attenuation of Ly α increases towards higher redshifts. We identify photometric galaxy overdensities near the z ≳ 7 Ly α emitters, potentially providing the ionizing flux necessary to create large ionized sightlines that facilitate Ly α transmission. Finally, we investigate the absence of Ly α emission in a comparable (and spectroscopically confirmed) galaxy overdensity at z = 7.88 in the Abell 2744 field, discussing new prism spectra of the field obtained with the UNCOVER program.

Unique distant classical Cepheid OGLE GD-CEP-1353 with anomalously high abundances of s- and r-process elements

Aims. While looking for recently discovered distant Cepheids with an interesting chemical composition, we noticed one star (OGLE GD-CEP-1353) with extremely large equivalent widths of spectral lines of heavy elements. The aim of this work is to perform an abundance analysis, and to find a possible explanation for the found chemical anomaly. Methods. Quantitative analysis of the equivalent widths and synthetic spectrum synthesis were used to derive abundances in this star. Both local and nonlocal thermodynamic equilibrium (LTE and NLTE) approximations were used in our analysis. Results. Abundances of 28 chemical elements from carbon to thorium were derived. While light and iron peak elements show abundances typical for distant Cepheids (located in the outer disk), the s-process elements are overabundant about one dex. r-process elements are slightly less overabundant. This makes the star a unique Cepheid of our Galaxy.

An extremely metal-poor star complex in the reionization era: Approaching Population III stars with JWST

We present JWST/Near Infrared Spectrograph (NIRSpec) integral field spectroscopy (IFS) of a lensed Population III candidate stellar complex (dubbed Lensed And Pristine 1, LAP1), with a lensing-corrected stellar mass of ≲104 M⊙ and an absolute luminosity of MUV &gt; −11.2 (mUV &gt; 35.6), confirmed at redshift 6.639 ± 0.004. The system is strongly amplified (μ ≳ 100) by straddling a critical line of the Hubble Frontier Field galaxy cluster MACS J0416. Although the stellar continuum is currently not detected in the Hubble and JWST/Near Infrared Camera (NIRCam) and Near Infrared Imager and Slitless Spectrograph (NIRISS) imaging, arclet-like shapes of Lyman and Balmer lines, Lyα, Hγ, Hβ and Hα are detected with NIRSpec IFS with signal-to-noise ratios (S/N) of approximately 5 − 13 and large equivalent widths (&gt; 300 − 2000 Å), along with a remarkably weak [O III]λλ4959, 5007 at S/N ≃ 4. LAP1 shows a large ionizing photon production efficiency, log(ξion[erg Hz−1]) &gt; 26. From the metallicity indexes R23 = ([O III] + [O II])/Hβ ≲ 0.74 and R3 = ([O III]/Hβ) = 0.55 ± 0.14, we derive an oxygen abundance of 12 + log(O/H)≲6.3. Intriguingly, the Hα emission is also measured in mirrored subcomponents where no [O III] is detected, providing even more stringent upper limits on the metallicity if in situ star formation is ongoing in this region (12 + log(O/H) &lt; 6). The formal stellar mass limit of the subcomponents would correspond to ∼103 M⊙ or MUV fainter than −10. Alternatively, this metal-free, pure line-emitting region could be the first case of a fluorescing H I gas region induced by transverse escaping ionizing radiation from a nearby star complex. The presence of large equivalent-width hydrogen lines and the deficiency of metal lines in such a small region make LAP1 the most metal-poor star-forming region currently known in the reionization era and a promising site that may host isolated, pristine stars.

Accurate systemic redshifts and outflow speeds for extremely red quasars (ERQs)

ABSTRACT Extremely Red Quasars (ERQs) are thought to represent a brief episode of young quasar and galactic evolution characterized by rapid outflows and obscured growth due to dusty environments. We use new redshift measurements from CO and narrow Ly α emission-lines to better constrain outflow velocities from previous line measurements. We present sample of 82 ERQs, and the analysis confirms that ERQs have a higher incidence of large C iv blueshifts, accompanied by large Rest Equivalent Width (REW) and narrower line Full Width at Half-Maximum (FWHM) than blue quasars. We find that strong blueshifts (&amp;gt;2000 km s−1) are present in 12/54 (22.2 per cent) of ERQs with the most robust redshift indicators. At least 4 out of 15 ERQs in the sample also have blueshifts in their H β and low-ionization ultraviolet lines ranging from −500 to −1500 km s−1. ERQs with strong C iv blueshifts are substantially offset in C iv REW and FWHM from typical blue quasars in the same velocity range. ERQs have average values of REW = 124 Å and FWHM = 5274 km s−1, while blue quasars have REW = 24 Å and FWHM = 6973 km s−1. The extreme nature of the outflows in ERQs might explain some of their other spectral properties, such as the large C iv REWs and peculiar wingless profiles owing to more extended broad-line regions participating in outflows. The physical reasons for the extreme outflow properties of ERQs are unclear; however, larger Eddington ratios and/or softer ionizing spectra incident on the outflow gas cannot be ruled out.

GA-NIFS: A massive black hole in a low-metallicity AGN atz ∼ 5.55 revealed by JWST/NIRSpec IFS

We present rest-frame optical data of the compactz = 5.55 galaxy GS_3073 obtained using the integral field spectroscopy mode of the Near-InfraRed Spectrograph on board theJames WebbSpace Telescope. The galaxy’s prominent broad components in several hydrogen and helium lines (though absent in the forbidden lines) and v detection of a large equivalent width of He IIλ4686, EW(He II) ∼20 Å, unambiguously identify it as an active galactic nucleus (AGN). We measured a gas phase metallicity ofZgas/Z⊙∼0.21−0.04+0.08, which is lower than what has been inferred for both more luminous AGN at a similar redshift and lower redshift AGN. We empirically show that classical emission line ratio diagnostic diagrams cannot be used to distinguish between the primary ionisation source (AGN or star formation) for systems with such low metallicity, though different diagnostic diagrams involving He IIλ4686 prove very useful, independent of metallicity. We measured the central black hole mass to be log(MBH/M⊙)∼8.2 ± 0.4 based on the luminosity and width of the broad line region of the Hαemission. While this places GS_3073 at the lower end of known high-redshift black hole masses, it still appears to be overly massive when compared to its host galaxy’s mass properties. We detected an outflow with a projected velocity ≳700 km s−1and inferred an ionised gas mass outflow rate of about 100 M⊙yr−1, suggesting that one billion years after the Big Bang, GS_3073 is able to enrich the intergalactic medium with metals.

Chemical Abundances of a Sample of Oxygen-dominated Galaxies

We spectroscopically analyzed a sample of 85 Sloan Digital Sky Survey compact, oxygen-dominated galaxies located at redshift z ∼ 0.001–0.350, selected because of their large equivalent width of [O iii]λ5007 (larger than 200 Å). These galaxies might be considered as extreme emission-line galaxies due to their strong [O iii]λ5007 emission line. We detected high-ionization lines, even those related to the presence of Wolf–Rayet stars, in almost all the galaxies studied. We obtained physical properties (electron density and temperature) as well as chemical abundances by using the direct method based on the electron temperature. In this analysis, we obtained three different measurements of T(high): the usual one, T([O iii]), but also that of T([S iii]) and T([Ar iii]) for five and three of the galaxies, respectively. Further, we established a new calibration for T([S iii]). We determined oxygen, nitrogen, sulfur, neon, argon, iron, and chlorine abundances when possible, and we compared to the results of other late-type, low-metallicity galaxies, such as blue compact dwarfs, Ims, and green peas. From such a detailed study, we can conclude that the majority of the galaxies in this sample have similar metallicities to the SMC (about ) ≈ 8 dex), and that only 12% of the galaxies are extremely metal-poor, with abundances lower than 7.7 dex. Also, a comparison with some chemical evolution models as well as a brief discussion on the chemical evolution with time is considered.

AGNs in the CALIFA survey: X-ray detection of nuclear sources

ABSTRACT A complete demographic of active galactic nuclei (AGNs) is essential to understand the evolution of the Universe. Optical surveys estimate the population of AGNs in the local Universe to be of ∼ 4 per cent. However, these results could be biased towards bright sources, not affected by the host galaxy attenuation. An alternative method for detecting these objects is through the X-ray emission. In this work, we aim to complement the AGN population of the optical CALIFA survey (941 sources), by using X-ray data from Chandra, which provides the best spatial resolution to date, essential to isolate the nuclear emission from the host galaxy. We study a total of 138 sources with available data. We find 34 new bona fide AGNs and 23 AGN candidates, which could increase the AGN population to 7–10 per cent among the CALIFA survey. X-rays are particularly useful for low-luminosity AGNs since they are excluded by the criterion of large equivalent width of the $\rm {H\alpha }$ emission line when applied to optical selections. Indeed, placing such a restrictive criteria might cause a loss of up to 70 per cent of AGN sources. X-ray detected sources are preferentially located in the right side of the [${\mathrm{O}}\, {\small {\rm III}}$ ]/Hβ versus [${\mathrm{N}}\, {\small {\rm II}}$ ]/Hα diagram, suggesting that this diagram might be the most reliable at classifying AGN sources. Our results support the idea that multiwavelength studies are the best way to obtain a complete AGN population.

Identification of large equivalent width dusty galaxies at 4 &lt; z &lt; 6 from sub-millimetre colours

Context. Infrared (IR), sub-millimetre (sub-mm), and millimetre (mm) databases contain a huge quantity of high-quality data. However, a large part of these data are photometric, and they are thought not to be useful to derive quantitative information on the nebular emission of galaxies. Aims. The aim of this project is first to identify galaxies at z ≳ 4–6 and in the epoch of reionisation from their sub-millimetre colours. We also aim to show that the colours can be used to try and derive physical constraints from photometric bands when accounting for the contribution from the IR fine structure lines to these photometric bands. Methods. We modelled the flux of IR fine structure lines with CLOUDY and added them to the dust continuum emission with CIGALE. Including (or not) emission lines in the simulated spectral energy distribution (SED) modifies the broad-band emission and colours. Results. The introduction of the lines allows us to identify strong star forming galaxies at z ≳ 4–6 from the [log10(PSW250μm)/(PMW350μm) versus log10(LABOCA870μm)/(PLW500μm)] colour-colour diagram. By comparing the relevant models to each observed galaxy colour, we are able to roughly estimate the fluxes of the lines and the associated nebular parameters. This method allows us to identify a double sequence in a plot built from the ionisation parameter and the gas metallicity. Conclusions. The HII and photodissociation region fine structure lines are an essential part of the SEDs. It is important to add them when modelling the spectra, especially at z ≳ 4–6, where their equivalent widths can be large. Conversely, we show that we can extract some information on strong-IR fine structure lines and on the physical parameters related to the nebular emission from IR colour-colour diagrams.

Extreme Nature of Four Blue-excess Dust-obscured Galaxies Revealed by Optical Spectroscopy

We report optical spectroscopic observations of four blue-excess dust-obscured galaxies (BluDOGs) identified by the Subaru Hyper Suprime-Cam. BluDOGs are a subclass of dust-obscured galaxies (DOGs; defined with the extremely red color (i − [22])AB ≥ 7.0; Toba et al., showing a significant flux excess in the optical g and r bands over the power-law fits to the fluxes at the longer wavelengths. Noboriguchi et al. have suggested that BluDOGs may correspond to the blowing-out phase involved in a gas-rich major-merger scenario. However, the detailed properties of BluDOGs are not understood because of the lack of spectroscopic information. In this work, we carry out deep optical spectroscopic observations of four BluDOGs using Subaru/FOCAS and VLT/FORS2. The obtained spectra show broad emission lines with extremely large equivalent widths, and a blue wing in the C iv line profile. The redshifts are between 2.2 and 3.3. The averaged rest-frame equivalent widths of the C iv lines are 160 ± 33 Å, ∼7 times higher than the average of a typical type 1 quasar. The FWHMs of their velocity profiles are between 1990 and 4470 km s−1, and their asymmetric parameters are 0.05 and 0.25. Such strong C iv lines significantly affect the broadband magnitudes, which are partly the origin of the blue excess seen in the spectral energy distribution of BluDOGs. Their estimated supermassive black hole masses are 1.1 × 108 < M BH/M ⊙ <5.5 × 108. The inferred Eddington ratios of the BluDOGs are higher than 1 (1.1 < λ Edd < 3.8), suggesting that the BluDOGs are in a rapidly evolving phase of supermassive black holes.

The Low-Redshift Lyman Continuum Survey

Aims. Combining 66 ultraviolet (UV) spectra and ancillary data from the recent Low-Redshift Lyman Continuum Survey (LzLCS) and 23 LyC observations by earlier studies, we form a statistical sample of star-forming galaxies at z ∼ 0.2 − 0.4 with which we study the role of cold interstellar medium (ISM) gas in the leakage of ionizing radiation. We also aim to establish empirical relations between the H I neutral and low-ionization state (LIS) absorption lines with different galaxy properties. Methods. We first constrain the massive star content (stellar ages and metallicities) and UV attenuation by fitting the stellar continuum with a combination of simple stellar population models. The models, together with accurate LyC flux measurements, allow us to determine the absolute LyC photon escape fraction for each galaxy (fescabs). We then measure the equivalent widths and residual fluxes of multiple H I and LIS lines, and the geometrical covering fraction of the UV emission, adopting the picket-fence model. Results. The LyC escape fraction spans a wide range, with a median fescabs (0.16, 0.84 quantiles) of 0.04 (0.02, 0.20), and 50 out of the 89 galaxies detected in the LyC (1σ upper limits of fescabs ≲ 0.01 for non-detections, typically). The H I and LIS line equivalent widths scale with the UV luminosity and attenuation, and inversely with the residual flux of these lines. Additionally, Lyα equivalent widths scale with both the H I and LIS residual fluxes, but anti-correlate with the corresponding H I or LIS equivalent widths. The H I and LIS residual fluxes are correlated, indicating that the neutral gas is spatially traced by the low-ionization transitions. We find that the observed trends of the absorption lines and the UV attenuation are primarily driven by the geometric covering fraction of the gas. The observed nonuniform gas coverage also demonstrates that LyC photons escape through low-column-density channels in the ISM. The equivalent widths and residual fluxes of both the H I and LIS lines strongly correlate with fescabs: strong LyC leakers (highest fescabs) show weak absorption lines, low UV attenuation, and large Lyα equivalent widths. We provide several empirical calibrations to estimate fescabs from UV absorption lines. Finally, we show that simultaneous UV absorption line and dust attenuation measurements can, in general, predict the escape fraction of galaxies. We apply our method to available measurements of UV LIS lines of 15 star-forming galaxies at z ∼ 4 − 6 (plus 3 high-z galaxy composites), finding that these high-redshift, UV-bright galaxies (MUV ≲ −21) may have low escape fractions, fescabs ≲ 0.1. Conclusions. UV absorption lines trace the cold ISM gas of galaxies, which governs the physics of the LyC escape. We show that, with some assumptions, the absolute LyC escape can be statistically predicted using UV absorption lines, and the method can be applied to study galaxies across a wide redshift range, including in the epoch of cosmic reionization.

Optical Characterization of Two Cataclysmic Variables: RBS 0490 and SDSS J075939.79+191417.3

We present optical photometric and spectroscopic observations of two cataclysmic variables (CVs), namely RBS 0490 and SDSS J075939.79+191417.3. The optical variations of RBS 0490 have been found to occur with a period of 1.689 ± 0.001 hr, which appears to be the probable orbital period of the system. Present photometric observations of SDSS J075939.79+191417.3 confirm and refine the previously determined orbital period as 3.14240928 ± 0.00000096 hr. The presence of long-duration eclipse features in the light curves of SDSS J075939.79+191417.3 indicates that eclipses might be due to an accretion disk and bright spot. The orbital inclination of SDSS J075939.79+191417.3 is estimated to be ∼78° using the eclipse morphology. The phased light-curve variations during the orbital cycle of RBS 0490 provide evidence of emission from an independent second accretion region or a second fainter pole. Optical spectra of RBS 0490 and SDSS J075939.79+191417.3 show the presence of strong Balmer and weak He ii (λ4686) emission lines, along with the detection of strong Hβ emission lines with a large equivalent width. The characteristic features of RBS 0490 seem to favor low-field polars, while SDSS J075939.79+191417.3 appears to be similar to nonmagnetic systems.

Cool circumgalactic gas in galaxy clusters: connecting the DESI legacy imaging survey and SDSS DR16 Mg ii absorbers

ABSTRACT We investigate the cool gas absorption in galaxy clusters by cross-correlating Mg ii absorbers detected in quasar spectra from data release 16 of the Sloan Digital Sky Survey (SDSS) with galaxy clusters identified in the Dark Energy Spectroscopic Instrument (DESI) survey. We find significant covering fractions ($1\!-\!5\, \mathrm{per\,cent}$ within r500, depending on the chosen redshift interval), ∼4–5 times higher than around random sightlines. While the covering fraction of cool gas in clusters decreases with increasing mass of the central galaxy, the total Mg ii mass within r500 is none the less ∼10 times higher than for SDSS luminous red galaxies. The Mg ii covering fraction versus impact parameter is well described by a power law in the inner regions and an exponential function at larger distances. The characteristic scale of the transition between these two regimes is smaller for large equivalent width absorbers. Cross-correlating Mg ii absorption with photo−$z$ selected cluster member galaxies from DESI reveals a statistically significant connection. The median projected distance between Mg ii absorbers and the nearest cluster member is ∼200 kpc, compared to ∼500 kpc in random mocks with the same galaxy density profiles. We do not find a correlation between Mg ii strength and the star formation rate of the closest cluster neighbour. This suggests that cool gas in clusters, as traced by Mg ii absorption, is: (i) associated with satellite galaxies, (ii) dominated by cold gas clouds in the intracluster medium, rather than by the interstellar medium of galaxies, and (iii) may originate in part from gas stripped from these cluster satellites in the past.

The Archival Discovery of a Strong Lyα and [C ii] Emitter at z = 7.677

Abstract We report the archival discovery of Lyα emission from the bright ultraviolet galaxy Y002 at z = 7.677, spectroscopically confirmed by its ionized carbon [C ii] 158 μm emission line. The Lyα line is spatially associated with the rest-frame UV stellar emission (M UV ∼ −22, 2× brighter than M UV ⋆ ), and it appears offset from the peak of the extended [C ii] emission at the current ∼1″ spatial resolution. We derive an estimate of the unobscured SFRUV = (22 ± 1) M ⊙ yr−1 and set an upper limit of SFRIR &lt; 15 M ⊙ yr−1 from the far-infrared (FIR) wavelength range, which globally places Y002 on the SFR(UV+IR)–L [C II] correlation observed at lower redshifts. In terms of velocity, the peak of the Lyα emission is redshifted by Δv Lyα ∼ 500 km s−1 from the systemic redshift set by [C ii] and a high-velocity tail extends up to ∼1000 km s−1. The velocity offset is up to ∼3.5× higher than the average estimate for similarly UV-bright emitters at z ∼ 6–7, which might suggest that we are witnessing the merging of two clumps. A combination of strong outflows and the possible presence of an extended ionized bubble surrounding Y002 would likely facilitate the escape of copious Lyα light, as indicated by the large equivalent width EW0(Lyα) = 24 − 6 + 5 Å. Assuming that [C ii] traces the neutral hydrogen, we estimate a H i gas fraction of M H I/M ⋆ ≳ 8 for Y002 as a system and speculate that patches of high H i column densities could contribute to explaining the observed spatial offsets between Lyα- and [C ii]-emitting regions. The low dust content, implied by the nondetection of the FIR continuum emission at rest frame ∼160 μm, would be sufficient to absorb any potential Lyα photons produced within the [C ii] clump as a result of large H i column densities.

An 8.56 keV Absorption Line in the Hyperluminous X-Ray Source in NGC 4045: Ultrafast Outflow or Cyclotron Line?

We report on the discovery of an absorption line at keV detected with a significance of >3.3σ in the NuSTAR and XMM-Newton spectra of a newly discovered hyperluminous X-ray source (L X > 1041 erg s−1) in the galaxy NGC 4045 at a distance of 32 Mpc. The source was first discovered serendipitously in a Swift/XRT observation of the galaxy, and Swift monitoring reveals a highly variable source changing by over an order of magnitude from maximum to minimum. The origin of the absorption line appears likely to be from highly ionized iron with a blueshift of 0.19c, indicating an ultrafast outflow. However, the large equivalent width of the line ( keV) paired with the lack of other absorption lines detected is difficult to reconcile with models. An alternative explanation is that the line is due to a cyclotron resonance scattering feature produced by the interaction of X-ray photons with the powerful magnetic field of a neutron star.

Equivalent widths of Lyman α emitters in MUSE-Wide and MUSE-Deep

Context. The hydrogen Lyman α line is often the only measurable feature in optical spectra of high-redshift galaxies. Its shape and strength are influenced by radiative transfer processes and the properties of the underlying stellar population. High equivalent widths of several hundred Å are especially hard to explain by models and could point towards unusual stellar populations, for example with low metallicities, young stellar ages, and a top-heavy initial mass function. Other aspects influencing equivalent widths are the morphology of the galaxy and its gas properties. Aims. The aim of this study is to better understand the connection between the Lyman α rest-frame equivalent width (EW0) and spectral properties as well as ultraviolet (UV) continuum morphology by obtaining reliable EW0 histograms for a statistical sample of galaxies and by assessing the fraction of objects with large equivalent widths. Methods. We used integral field spectroscopy from the Multi Unit Spectroscopic Explorer (MUSE) combined with broad-band data from the Hubble Space Telescope (HST) to measure EW0. We analysed the emission lines of 1920 Lyman α emitters (LAEs) detected in the full MUSE-Wide (one hour exposure time) and MUSE-Deep (ten hour exposure time) surveys and found UV continuum counterparts in archival HST data. We fitted the UV continuum photometric images using the Galfit software to gain morphological information on the rest-UV emission and fitted the spectra obtained from MUSE to determine the double peak fraction, asymmetry, full-width at half maximum, and flux of the Lyman α line. Results. The two surveys show different histograms of Lyman α EW0. In MUSE-Wide, 20% of objects have EW0 &gt; 240 Å, while this fraction is only 11% in MUSE-Deep and ≈16% for the full sample. This includes objects without HST continuum counterparts (one-third of our sample), for which we give lower limits for EW0. The object with the highest securely measured EW0 has EW0 = 589 ± 193 Å (the highest lower limit being EW0 = 4464 Å). We investigate the connection between EW0 and Lyman α spectral or UV continuum morphological properties. Conclusions. The survey depth has to be taken into account when studying EW0 distributions. We find that in general, high EW0 objects can have a wide range of spectral and UV morphological properties, which might reflect that the underlying causes for high EW0 values are equally varied.

High star cluster formation efficiency in the strongly lensed Sunburst Lyman-continuum galaxy at z = 2.37

We investigate the strongly lensed (μ ≃ ×10 − 100) Lyman continuum (LyC) galaxy, dubbed Sunburst, at z = 2.37, taking advantage of a new accurate model of the lens. A characterization of the intrinsic (delensed) properties of the system yields a size of ≃3 sq. kpc, a luminosity of MUV = −20.3, and a stellar mass of M ≃ 109 M⊙; 16% of the ultraviolet light is located in a 3 Myr old gravitationally bound young massive star cluster (YMC), with an effective radius of ∼8 pc (corresponding to 1 milliarcsec without lensing) and a dynamical mass of ∼107 M⊙ (similar to the stellar mass) – from which LyC radiation is detected (λ &lt; 912 Å). The star formation rate and stellar mass surface densities for the YMC are Log10(ΣSFR[M⊙ yr−1 kpc−2]) ≃ 3.7 and Log10(ΣM[M⊙ pc−2]) ≃ 4.1, with sSFR &gt; 330 Gyr−1, consistent with the values observed in local young massive star clusters. The inferred outflowing gas velocity (&gt; 300 km s−1) exceeds the escape velocity of the cluster. The resulting relative escape fraction of the ionizing radiation emerging from the entire galaxy is higher than 6−12%, whilst it is ≳46 − 93% if inferred from the YMC multiple line of sights. At least 12 additional unresolved star-forming knots with radii spanning the interval 3 − 20 pc (the majority of them likely gravitationally bound star clusters) are identified in the galaxy. A significant fraction (40−60%) of the ultraviolet light of the entire galaxy is located in such bound star clusters. In adopting a formation timescale of the star clusters of 20 Myr, a cluster formation efficiency Γ ≳ 30%. The star formation rate surface density of the Sunburst galaxy (Log10(ΣSFR) = 0.5−0.2+0.3) is consistent with the high inferred Γ, as observed in local galaxies experiencing extreme gas physical conditions. Overall, the presence of a bursty event (i.e., the 3 Myr old YMC with large sSFR) significantly influences the morphology (nucleation), photometry (photometric jumps), and spectroscopic output (nebular emission) of the entire galaxy. Without lensing magnification, the YMC would be associated to an unresolved 0.5 kpc–size star-forming clump. The delensed LyC and UV magnitude m1600 (at 1600 Å) of the YMC are ≃30.6 and ≃26.9, whilst the entire galaxy has m1600 ≃ 24.8. The Sunburst galaxy shows a relatively large rest-frame equivalent width of EWrest(Hβ + [O III]λλ4959, 5007) ≃ 450 Å, with the YMC contributing to ∼30% (having a local EWrest ≃ 1100 Å) and ∼1% of the total stellar mass. If O-type (ionizing) stars are mainly forged in star clusters, then such engines were the key ionizing agents during reionization and the increasing occurrence of high equivalent width lines (Hβ + [O III]) observed at z &gt; 6.5 might be an indirect signature of a high frequency of forming massive star clusters (or high Γ) at reionization. Future facilities, which will perform at few tens milliarcsec resolution (e.g., VLT/MAVIS or ELT), will probe bound clusters on moderately magnified (μ &lt; 5 − 10) galaxies across cosmic epochs up to reionization.

A Suzaku sample of unabsorbed narrow-line and broad-line Seyfert 1 galaxies – II. Iron emission and absorption

ABSTRACTA sample of 22 narrow-line type 1 Seyfert (NLS1) and 47 broad-line type 1 Seyfert (BLS1) galaxies observed with Suzaku is used to examine the Fe K-band properties of each group. Three different models are used to examine the presence of: narrow neutral Fe K α line at $6.4{\rm \, keV}$ and ionized Fe xxv and Fe xxvi emission lines (model A); a broad emission feature at around $6{-}7{\rm \, keV}$ (model B); and an absorption edge at ${\sim}7.1{\rm \, keV}$ (model C). In all three models, the neutral Fe K α line is weaker (lower luminosity and equivalent width) in NLS1s than in BLS1s. Model (B) also finds a more significant broad component (larger equivalent width) in NLS1s than in BLS1s. The feature does not appear to be an artifact of steeper spectra in NLS1s, but rather an intrinsic property of these sources. From model (C), the optical depth of the absorption edge appears comparable between the two samples. When comparing the absorption with the emission line properties, NLS1s seem to exhibit a lower ratio of emission-to-absorption of iron than BLS1s, and have a lower value than expected based on the fluorescence yield. The observed differences may arise from different torus geometries (e.g. larger opening angle in NLS1s), and/or additional sources of Fe K emission and absorption in NLS1s beyond pure fluorescence (e.g. originating in the disc and broad-line region).