Spectral Energy Distribution Modeling Research Articles

Flexible Models for Galaxy Star Formation Histories Both Shift and Scramble the Optical Color–Mass-to-light Ratio (M/L) Relationship

The remarkably tight relationship between galaxy optical color and stellar mass-to-light ratio (M */L) is widely used for efficient stellar mass estimates. However, it remains unclear whether this low scatter comes from a natural order in the galaxy population, or whether it is driven by simple relationships in the models used to describe them. In this work, we investigate the origins of the relationship by contrasting the derived relationship from a simple 4 parameter spectral energy distribution (SED) model with a more sophisticated 14D Prospector–α model including nonparametric star formation histories (SFHs). We apply these models to 63,430 galaxies at 0.5 < z < 3 and fit a hierarchical Bayesian model (HBM) to the population distribution in the (g − r)– plane. We find that Prospector–α infers systematically higher M */L by 0.12 dex, a result of nonparametric SFHs producing older ages, and also systematically redder rest frame (g − r) by 0.06 mag owing to the contribution from nebular emission. Surprisingly, the combined effects of the M */L and (g − r) offsets produce a similar average relationship for the two models; though Prospector–α produces a higher scatter of 0.28 dex compared to the simple model of 0.12 dex. Also, unlike the simple model, the Prospector–α relationship shows substantial redshift evolution due to stellar aging. These expected and testable effects produce overall older and redder galaxies; though the color–M */L relationship is measured only at 0.5 < z < 3. Finally, we demonstrate that the HBM produces substantial shrinkage in the individual posteriors of faint galaxies, an important first step toward using the observed galaxy population directly to inform the SED-fitting priors.

Photometric studies on the host galaxies of gamma-ray bursts using 3.6m Devasthal optical telescope

In this article, we present multi-band photometric observations and analysis of the host galaxies for a sample of five interesting gamma-ray bursts (GRBs) observed using the 3.6m Devasthal Optical Telescope (DOT) and the back-end instruments. The host galaxy observations of GRBs provide unique opportunities to estimate the stellar mass, ages, star-formation rates, and other vital properties of the burst environments and hence progenitors. We performed a detailed spectral energy distribution (SED) modeling of the five host galaxies using an advanced tool called Prospector, a stellar population synthesis model. Furthermore, we compared the results with a larger sample of well-studied host galaxies of GRBs, supernovae, and normal star-forming galaxies. Our SED modeling suggests that GRB 130603B, GRB 140102A, GRB 190829A, and GRB 200826A have massive host galaxies with high star formation rates (SFRs). On the other hand, a supernovae-connected GRB 030329 has a rare low-mass galaxy with a low star formation rate. We also find that GRB 190829A has the highest (in our sample) amount of visual dust extinction and gas in its local environment of the host, suggesting that the observed very high energy emission from this burst might have a unique local environment. Broadly, the five GRBs in our sample satisfy the typical correlations between host galaxies parameters and these physical parameters are more common to normal star-forming galaxies at the high-redshift Universe. Our results also demonstrate the capabilities of 3.6m DOT and the back-end instruments for the deeper photometric studies of the host galaxies of energetic transients such as GRBs, supernovae, and other transients in the long run.

Measuring Protoplanetary Disk Dust Masses in Lupus with Spectral Energy Distribution Modeling

Measuring Protoplanetary Disk Dust Masses in Lupus with Spectral Energy Distribution Modeling

A Machine Learning Approach for Predicting Black Hole Mass in Blazars Using Broadband Emission Model Parameters

Blazars are observed to emit non-thermal radiation across the entire electromagnetic spectrum from the radio to the very-high-energy γ-ray region. The broadband radiation measured from a blazar is dominated by emission from a relativistic plasma jet which is assumed to be powered by a spinning supermassive black hole situated in the central region of the host galaxy. The formation of jets, their mode of energy transport, actual power budget, and connection with the central black hole are among the most fundamental open problems in blazar research. However, the observed broadband spectral energy distribution from blazars is generally explained by a simple one-zone leptonic emission model. The model parameters place constraints on the contributions from the magnetic field, radiation field, and kinetic power of particles to the emission region in the jet. This in turn constrains the minimum power transported by the jet from the central engine. In this work, we explore the potential of machine learning frameworks including linear regression, support vector machine, adaptive boosting, bagging, gradient boosting, and random forests for the estimation of the mass of the supermassive black hole at the center of the host galaxy of blazars using the best-fit emission model parameters derived from the broadband spectral energy distribution modeling in the literature. Our study suggests that the support vector machine, adaptive boosting, bagging, and random forest algorithms can predict black hole masses with reasonably good accuracy.

Long-Term Monitoring of Blazar PKS 0208-512: A Change of γ-Ray Baseline Activity from EGRET to Fermi Era

The blazar PKS 0208-512 was in the lowest γ-ray brightness state during the initial 10 years of observations with the Fermi Gamma-ray Space Telescope (Fermi), which was an order of magnitude lower than its flux state during the EGRET era (1991–2000). The weekly averaged maximum γ-ray flux of this source during the first 10 years of Fermi observation is nearly a factor of 3 lower than the highest flux observed by EGRET in a single epoch. During the period 2018–2020, the source showed a large γ-ray flare, with the average brightness similar to the period 1991–2000. We observed the source with AstroSat, during its low and high activity states, respectively. We carried out broad-band spectral energy distribution (SED) modeling of the source using a one-zone leptonic emission model during its various brightness states. From the SED modeling, we found that there was an inefficient conversion from the bulk energy to the particle energy during the long-term low-activity states as compared to the high flux state during the EGRET era and the later part of Fermi observation.

The recent star formation history of NGC 628 on resolved scales

ABSTRACT Star formation histories (SFHs) are integral to our understanding of galaxy evolution. We can study recent SFHs by comparing the star formation rate (SFR) calculated using different tracers, as each probes a different time-scale. We aim to calibrate a proxy for the present-day rate of change in SFR, dSFR/dt, which does not require full spectral energy distribution (SED) modelling and depends on as few observables as possible, to guarantee its broad applicability. To achieve this, we create a set of models in cigale and define an SFR change diagnostic as the ratio of the SFR averaged over the past 5 and 200 Myr, $\langle SFR_{\rm {5}} \rangle \big / \langle SFR_{\rm {200}} \rangle$, probed by the H α–FUV colour. We apply $\langle SFR_{\rm {5}} \rangle \big / \langle SFR_{\rm {200}} \rangle$ to the nearby spiral NGC 628 and find that its star formation activity has overall been declining in the recent past, with the spiral arms, however, maintaining a higher level of activity. The impact of the spiral arm structure is observed to be stronger on $\langle SFR_{\rm {5}} \rangle \big / \langle SFR_{\rm {200}} \rangle$ than on the star formation efficiency. In addition, increasing disc pressure tends to increase recent star formation, and consequently $\langle SFR_{\rm {5}} \rangle \big / \langle SFR_{\rm {200}} \rangle$. We conclude that $\langle SFR_{\rm {5}} \rangle \big / \langle SFR_{\rm {200}} \rangle$ is sensitive to the molecular gas content, spiral arm structure, and disc pressure. The $\langle SFR_{\rm {5}} \rangle \big / \langle SFR_{\rm {200}} \rangle$ indicator is general and can be used to reconstruct the recent SFH of any star-forming galaxy for which H α, FUV, and either mid- or far-IR photometry is available, without the need of detailed modelling.

Low-frequency Radio Continuum Imaging and SED Modeling of 11 LIRGs: Radio-only and FUV to Radio Bands

We present a detailed analysis of 11 local luminous infrared galaxies from ultraviolet through far-infrared to radio (∼70 MHz to ∼15 GHz) bands. We derive the astrophysical properties through spectral energy distribution (SED) modeling using the Code Investigating GALaxy Emission (CIGALE) and UltraNest codes. The radio SEDs include our new observations at 325 and 610 MHz from the GMRT and the measurements from public archives. Our main results are (1) radio SEDs show turnovers and bends, (2) the synchrotron spectral index of the fitted radio spectra ranges between −0.5 and −1.7, and (3) the infrared luminosity, dust mass, dust temperature, stellar mass, star formation rates (SFRs), and active galactic nuclei (AGN) fraction obtained from CIGALE fall within the range exhibited by galaxies of the same class. The ratio of 60 μm infrared and 1.4 GHz radio luminosity, the 1.4 GHz thermal fraction, and emission measure range between 2.1 and 2.9, 0.1% and 10%, 0.02 and 269.5 × 106 cm−6 pc, respectively. We conclude that the turnovers seen in the radio SEDs are due to free–free absorption; this is supported by the low AGN fraction derived from the CIGALE analysis. The decomposed 1.4 GHz thermal and nonthermal radio luminosities allowed us to compute the SFR using scaling relations. A positive correlation is observed between the SFRIR obtained 10 Myr ago (compared to 100 Myr ago) and 1.4 GHz radio (total and nonthermal) because similar synchrotron lifetimes are expected for typical magnetic field strengths observed in these galaxies (≈50 μG).

Variability and Spectral Behavior of Gamma-Ray Flares of 3C 279

3C 279 showed enhanced flux variations in Fermi-LAT γ-ray observations from 2018 January to June. We present a detailed Fermi-LAT analysis to investigate the variability and spectral behaviors of 3C 279 during the γ-ray flares in 2018. In this work, we analyzed the γ-ray spectra and found that the spectra in either the flaring or quiescent states do not show any clear breaks (or cutoffs). This indicates that the dissipation region is outside the broad-line region, and the energy dissipation may be due to the inverse Compton process of scattering the dust torus infrared photons, this result is also consistent with that in Tolamatti et al. An external inverse Compton scattering of dusty torus (DT) photons is employed to calculate the broadband spectral energy distribution (SED). This model was further supported by the fact that we found flare decay timescale was consistent with the cooling time of relativistic electrons through DT photons. During the SED modeling, a relatively harder spectrum for the electron energy distribution is found and suggests these electrons may not be accelerated by the shock that happened in the dissipation region. Besides, the magnetic reconnection is also ruled out due to a low magnetization ratio. Thus, we suggest an injection of higher-energy electrons from outside the blob and raising the flare.

Strong C iv emission from star-forming galaxies: a case for high Lyman continuum photon escape

ABSTRACT Finding reliable indicators of Lyman continuum (Ly C) photon leakage from galaxies is essential in order to infer their escape fraction in the epoch of reionization, where direct measurements of Ly C flux are impossible. To this end, here we investigate whether strong C iv λλ1548, 1550 emission in the rest-frame UV spectra of galaxies traces conditions ripe for ample production and escape of Ly C photons. We compile a sample of 19 star-forming galaxies in the redshift range $z$ = 3.1–4.6 from the VANDELS survey that exhibit strong C iv emission, producing a stacked spectrum where all major rest-UV emission lines are clearly detected. Best-fitting spectral energy distribution models containing both stellar and nebular emission suggest the need for low stellar metallicities ($Z=0.1--0.2\, Z_\odot$), young stellar ages ($\log (\rm {age\,yr^{-1}}) = 6.1--6.5$), a high ionization parameter (log U = −2) and little to no dust attenuation (E(B − V) = 0.00–0.01). However, these models are unable to fully reproduce the observed C iv and He ii line strengths. We find that the Ly α line in the stacked spectrum is strong and peaks close to the systemic velocity, features that are indicative of significant Ly C photon leakage along the line of sight. The covering fractions of low-ionization interstellar absorption lines are also low, implying Ly C escape fraction in the range ≈0.05–0.30, with signatures of outflowing gas. Finally, C iv/C iii] ratios of &amp;gt;0.75 for a subset of individual galaxies with reliable detections of both lines are also consistent with physical conditions that enable significant Ly C leakage. Overall, we report that multiple spectroscopic indicators of Ly C leakage are present in the stacked spectrum of strong C iv emitting galaxies, potentially making C iv an important tracer of Ly C photon escape at $z$ &amp;gt; 6.

Multiwavelength Modeling the SED of Luminous Supersoft X-Ray Sources in Large Magellanic Cloud and Small Magellanic Cloud

Classical supersoft X-ray sources (SSSs) are understood as close binary systems in which a massive white dwarf accretes from its companion at rates sustaining steady hydrogen burning on its surface generating bolometric luminosities of 1036–2 × 1038 erg s−1. Here, we perform for the first time the global supersoft X-rays to near-infrared (NIR) spectral energy distribution (SED) for the brightest SSSs in the Large Magellanic Cloud and Small Magellanic Cloud. We test a model in which the ultraviolet–NIR is dominated by emission from a compact (unresolved) circumstellar nebula represented by the ionized gas outflowing from the SSS. The SED models correspond to luminosities of SSSs of a few times 1038–1039 erg s−1, radiating at blackbody temperatures of ≈3 × 105 K, and indicate a nebular continuum, whose emission measure of ≳2 × 1060 cm−3 corresponds to a wind mass loss at rates ≳2 × 10−6 M ⊙ yr−1. Such extreme parameters suggest that the brightest SSSs could be unidentified optical novae in a post-nova SSS state sustained at a high long-lasting luminosity by resumed accretion, possibly at super-Eddington rates. New observations and theoretical multiwavelength modeling of the global SED of SSSs are needed to reliably determine their parameters, and thus understand their proper stage in stellar evolution.

The MOSDEF survey: towards a complete census of the z ∼ 2.3 star-forming galaxy population

ABSTRACT We analyse the completeness of the MOSDEF survey, in which z ∼ 2 galaxies were selected for rest-optical spectroscopy from well-studied HST extragalactic legacy fields down to a fixed rest-optical magnitude limit (HAB = 24.5). The subset of z ∼ 2 MOSDEF galaxies with high signal-to-noise (S/N) emission-line detections analysed in previous work represents a small minority (&amp;lt;10 per cent) of possible z ∼ 2 MOSDEF targets. It is therefore crucial to understand how representative this high S/N subsample is, while also more fully exploiting the MOSDEF spectroscopic sample. Using spectral-energy distribution (SED) models and rest-optical spectral stacking, we compare the MOSDEF z ∼ 2 high S/N subsample with the full MOSDEF sample of z ∼ 2 star-forming galaxies with redshifts, the latter representing an increase in sample size of more than a factor of three. We find that both samples have similar emission-line properties, in particular in terms of the magnitude of the offset from the local star-forming sequence on the [N ii] BPT diagram. There are small differences in median host galaxy properties, including the stellar mass (M*), star formation rate (SFR) and specific SFR (sSFR), and UVJ colours; however, these offsets are minor considering the wide spread of the distributions. Using SED modelling, we also demonstrate that the sample of z ∼ 2 star-forming galaxies observed by the MOSDEF survey is representative of the parent catalog of available such targets. We conclude that previous MOSDEF results on the evolution of star-forming galaxy emission-line properties were unbiased relative to the parent z ∼ 2 galaxy population.

Investigating the Origin of X-Ray Jets: A Case Study of Four Hybrid Morphology MOJAVE Blazars

We carried out Chandra, Hubble Space Telescope (HST), and Very Large Array observations of four MOJAVE blazars that have previously been classified as hybrid (FR I/II) blazars in terms of radio morphology but not total radio power. The motivation of this study is to determine the X-ray emission mechanism in jets, these being different in FR I and FR II jets. We detected X-ray jet emission with sufficient signal to noise in two blazars, viz. PKS 0215+015 and TXS 0730+504. We carried out spectral energy distribution modeling of the broadband emission from the jet regions in these sources and found that a single synchrotron emission model is ruled out due to the deep upper limits obtained from HST optical and IR data. The inverse Compton-cosmic microwave background model can reproduce the X-ray jet emission in both sources although the model requires extreme jet parameters. Both our sources possess FR II-like radio powers and our results are consistent with previous studies suggesting that radio power is more important than FR morphology in determining the emission mechanism of X-ray jets.

Paving the way forEuclid and JWST via probabilistic selection of high-redshift quasars

ABSTRACT We introduce a probabilistic approach to select 6 ≤ $z$ ≤ 8 quasar candidates for spectroscopic follow-up, which is based on density estimation in the high-dimensional space inhabited by the optical and near-infrared photometry. Densities are modelled as Gaussian mixtures with principled accounting of errors using the extreme deconvolution (XD) technique, generalizing an approach successfully used to select lower redshift ($z$ ≤ 3) quasars. We train the probability density of contaminants on 1902 071 7-d flux measurements from the 1076 deg2 overlapping area from the Dark Energy Camera Legacy Survey (DECaLS) ($z$), VIKING (YJHKs), and unWISE (W1W2) imaging surveys, after requiring they dropout of DECaLS g and r, whereas the distribution of high-$z$ quasars are trained on synthetic model photometry. Extensive simulations based on these density distributions and current estimates of the quasar luminosity function indicate that this method achieves a completeness of $\ge 56{{\ \rm per\ cent}}$ and an efficiency of $\ge 5{{\ \rm per\ cent}}$ for selecting quasars at 6 &amp;lt; $z$ &amp;lt; 8 with JAB &amp;lt; 21.5. Among the classified sources are 8 known 6 &amp;lt; $z$ &amp;lt; 7 quasars, of which 2/8 are selected suggesting a completeness $\simeq 25{{\ \rm per\ cent}}$, whereas classifying the 6 known (JAB &amp;lt; 21.5) quasars at $z$ &amp;gt; 7 from the entire sky, we select 5/6 or a completeness of $\simeq 80{{\ \rm per\ cent}}$. The failure to select the majority of 6 &amp;lt; $z$ &amp;lt; 7 quasars arises because our quasar density model is based on an empirical quasar spectral energy distribution model that underestimates the scatter in the distribution of fluxes. This new approach to quasar selection paves the way for efficient spectroscopic follow-up of Euclid quasar candidates with ground-based telescopes and James Webb Space Telescope.

Multiwavelength temporal and spectral study of TeV blazar 1ES 1727+502 during 2014–2021

ABSTRACT One of the most important questions in blazar physics is the origin of broad-band emission and fast-flux variation. In this work, we studied the broad-band temporal and spectral properties of a TeV blazar 1ES 1727+502 and explore the one-zone synchrotron self-Compton (SSC) model to fit the broad-band spectral energy distribution (SED). We collected the long-term (2014–2021) multiband data that include both the low- and high-flux states of the source. The entire light curve is divided into three segments of different flux states and the best-fitting parameters obtained by broad-band SED modelling corresponding to three flux states were then compared. The TeV blazar 1ES 1727+502 has been observed to show the brightest flaring episode in the X-ray followed by the optical–UV and γ-rays. The fractional variability estimated during various segments behaves differently in multiple wavebands, suggesting a complex nature of emission in this source. This source has shown a range of variability time from days scale to month scale during this long period of observations between 2014 and 2021. A ‘harder-when-brighter’ trend is not prominent in the X-ray but seen in the optical–UV and an opposite trend is observed in the γ-ray. The complex nature of correlation among various bands is observed. The SED modelling suggests that the one-zone SSC emission model can reproduce the broad-band spectrum in the energy range from optical–UV to very high energy γ-ray.

The ALPINE-ALMA [C II] survey. Dust attenuation curves at z = 4.4–5.5

Context. There is ample evidence that dust is already present in abundance at high redshift. However, given the faintness of distant galaxies in the optical and the near-infrared, the data are limited and the understanding of how the dust affects the emerging radiation of galaxies at very high redshift is still limited. Aims. Using the ALMA Large Program to INvestigate [C II] at Early times (ALPINE), our objective is to quantify the dust attenuation properties in galaxies at z = 4.4–5.5, particularly with regard to the shape of their attenuation curve. Methods. Using the CIGALE spectral energy distribution (SED) code, we modeled the stellar populations and their interactions with the dust to measure some of the physical properties of the ALPINE sample. We selected a subsample of 23 main-sequence galaxies requiring a detection in at least six bands in the rest-frame UV and optical, as well as in the dust continuum around 158 μm or the [C II] fine-structure line. The inclusion of this line is important for improving the constraints on the physical properties, while achieving a reasonably low uncertainty on the slope of the attenuation curves. Results. We find that the attenuation curves span a broad range of properties – from curves that are much steeper than the SMC extinction curve to those that are shallower than the starburst attenuation curve. The shape of the attenuation curves strongly depends on the V-band attenuation. Galaxies with the lowest attenuation also present the steepest curves. The steepness of such curves probably results from the combination of the intrinsic physical properties of the dust, the relative distribution of stars and dust in the interstellar medium, and the differential reddening, with an important fraction of the dust concentrated in star-forming regions. The broad range of attenuation curves found at z ∼ 5 shows that no single attenuation curve is appropriate for main-sequence galaxies. When SED modeling is not feasible, assuming a fixed curve can lead to large errors, for instance, in the interpretation and application of the IRX-β diagram. Conclusions. Considerable caution should be exercised when correcting high redshift galaxies for the presence of dust using the UV slope β as it can affect the estimation of both star formation rates and stellar mass even at low V-band attenuation due to the steepness of the attenuation curve. However, when SED modeling can be used, the impact of the choice of the attenuation curve on the star formation rate and the stellar mass is limited.

Variable Active Galactic Nuclei in the Galaxy Evolution Explorer Time Domain Survey

We searched the northern hemisphere fields of the Galaxy Evolution Explorer Time Domain Survey for galaxies with UV variability indicative of active galactic nuclei (AGNs). We identified 48 high-probability candidate AGNs from a parent sample of 1819 galaxies in the NASA Sloan Atlas catalog. We further characterized these systems using optical spectroscopic diagnostics, Wide-field Infrared Survey Explorer IR color selection criteria, and spectral energy distribution modeling. Of the 48 candidates, eight were identified as AGNs from optical emission lines, two were identified by their IR colors, and 28 were identified through spectral energy decomposition. Observational biases of each selection method are discussed in connecting these AGN subsamples to another. By selecting AGNs based on UV variability, we also identified six low-mass AGN candidates, all of which would have been missed by spectroscopic selection.

Subarcsecond view on the high-redshift blazar GB 1508+5714 by the International LOFAR Telescope

Context. Studies of the most distant active galactic nuclei (AGNs) allow us to test our current understanding of the physics present in radio-jetted AGNs across a range of environments, and probe their interactions with these environments. The decrease in apparent luminosity with distance is the primary difficulty to overcome in the study of these distant AGNs, which requires highly sensitive instruments. Aims. Our goal is to employ new long wavelength radio data to better parametrise the broad-band spectral energy distribution (SED) of GB 1508+5714, a high-redshift (z = 4.30) AGN. Its high redshift, high intrinsic luminosity and classification as a blazar allow us to test emission models that consider the efficient cooling of jet electrons via inverse Compton losses in interactions with the dense cosmic microwave background (CMB) photon field at high redshifts. A significant detection of this effect in GB 1508+5714 may partly explain the apparent sparsity of high-redshift radio galaxies in wide-field surveys, detections of this kind are only becoming possible with the current generation of Square Kilometre Array (SKA) precursors. Methods. We used the LOw-Frequency ARray (LOFAR) to image the long wavelength radio emission around the high-redshift blazar GB 1508+5714 on arcsecond scales at frequencies between 128 and 160 MHz. This allowed us to compare the spatially resolved structure with higher frequency observations, and construct spectral index maps to study the spectral properties of the different components. Results. The LOFAR image shows a compact unresolved core and two resolved emission regions around 2 arcsec to the east and to the west of the radio core. We find structure consistent with previous Very Large Array (VLA) observations, as well as a previously unreported emission region to the east. The region in the west shows a spectral index of −1.2−0.2+0.4 while the region in the east indicates a spectral index of ≲−1.1. The radio core features aflat spectral index of 0.02 ± 0.01. Conclusions. We interpret the arcsecond-scale radio structure of GB 1508+5714 as a FR II-like radio galaxy at a small viewing angle, and the western component as the region containing the approaching jet’s terminal hot spot while the eastern diffuse component near the core can be interpreted as the counter-hot spot region. Our SED modelling shows that a scenario featuring significant quenching effects caused by interaction with the CMB provides a good description of the data, and notably explains the suppressed radio emission.

The thesan project: predictions for multitracer line intensity mapping in the epoch of reionization

ABSTRACT Line intensity mapping (LIM) is rapidly emerging as a powerful technique to study galaxy formation and cosmology in the high-redshift Universe. We present LIM estimates of select spectral lines originating from the interstellar medium (ISM) of galaxies and 21 cm emission from neutral hydrogen gas in the Universe using the large volume, high resolution thesan reionization simulations. A combination of subresolution photoionization modelling for H ii regions and Monte Carlo radiative transfer calculations is employed to estimate the dust-attenuated spectral energy distributions (SEDs) of high-redshift galaxies (z ≳ 5.5). We show that the derived photometric properties such as the ultraviolet (UV) luminosity function and the UV continuum slopes match observationally inferred values, demonstrating the accuracy of the SED modelling. We provide fits to the luminosity–star formation rate relation (L–SFR) for the brightest emission lines and find that important differences exist between the derived scaling relations and the widely used low-z ones because the ISM of reionization era galaxies is generally less metal enriched than in their low-redshift counterparts. We use these relations to construct line intensity maps of nebular emission lines and cross-correlate with the 21 cm emission. Interestingly, the wavenumber at which the correlation switches sign (ktransition) depends heavily on the reionization model and to a lesser extent on the targeted emission line, which is consistent with the picture that ktransition probes the typical sizes of ionized regions. The derived scaling relations and intensity maps represent a timely state-of-the-art framework for forecasting and interpreting results from current and upcoming LIM experiments.

Toward Understanding the B[e] Phenomenon. VIII. Nature and Variability of IRAS 07080+0605

We report the results of spectroscopic and photometric observations of the emission-line object IRAS 07080+0605 carried out in 2004–2021. We found that the object is significantly underluminous for its spectroscopic properties (T eff = 8500 ± 500 K, g = 2.0 ± 0.5), if a strong visual attenuation by a factor of ∼43 found through the spectral energy distribution modeling is not taken into account. Visual brightness variations with a stable period of 190 days but a variable amplitude of ∼0.2 mag were found in the ASAS SN data and attributed to variable circumstellar extinction in the dusty disk. We also found that the observed behavior of IRAS 07080+0605 is similar to that of the protoplanetary nebula Red Rectangle. The dusty disk of IRAS 07080+0605 shows the presence of carbonaceous particles (∼10%–20% of the total dust content) and polycyclic aromatic hydrocarbon emission bands. However, IRAS 07080+0605 shows no obvious signs of the refractory element depletion, which is common in post–asymptotic giant branch (AGB) dusty binaries, or of a visual nebula. Absorption-line positions vary with an amplitude of ∼25 km s−1, suggesting the presence of a secondary component. Spectroscopic monitoring on a timescale from days to months is needed to search for regular variations. We conclude that IRAS 07080+0605 is most likely a binary system with an A-type component on its way toward the post-AGB evolutionary stage, as binarity is capable of explaining most of the observed features.

CRIRES high-resolution near-infrared spectroscopy of diffuse interstellar band profiles

Aims. A high spectral resolution investigation of diffuse interstellar bands (DIBs) in the near-infrared (YJ band) is conducted to test new methods, to confirm and improve existing parameters, and to search for new DIBs. Methods. The CRyogenic high-resolution InfraRed Echelle Spectrograph (CRIRES) on the European Southern Observatory's Very Large Telescope was employed to obtain spectra of four reddened background supergiant stars (HD 183143, HD 165784, HD 92207, HD 111613) and an unreddened comparison star (HD 87737) at the highest resolution of R ≈ 100 000 currently achievable at near-infrared wavelengths, more than twice as high as accomplished in previous near-infrared DIB studies. The correction for telluric absorption was performed by a modelling approach. Non-local thermodynamic equilibrium spectral modelling of available optical and the new near-infrared stellar spectra facilitated a comprehensive characterisation of the atmospheric properties of the background stars. As a consequence, a more precise and accurate determination of the reddening and the reddening law along the respective sight lines could be achieved than feasible before by comparison of the observed and model spectral energy distributions. For DIBs that overlap with stellar lines the DIB profile shapes could be recovered. Results. Seventeen known near-infrared DIBs were confirmed, and 12 previously unknown and generally weaker DIBs were identified in the YJ band. Three DIBs that show uniform profiles along all sight lines were identified, possibly connected to transitions from a common lower state of the same carrier. The divergent extinction curve towards the frequently discussed DIB standard star HD 183143 could be reproduced for the first time, requiring extra absorption by ~3.5 mag due to polycyclic aromatic hydrocarbons (PAHs) to match the ultraviolet extinction bump. This extra absorption probably stems from a circumstellar bubble lying in front of the star which is intersected tangentially by the line of sight, making this particular sight line more peculiar than standard.