arXiv subjects

Henrik Spoon

Publications and source records attributed to Henrik Spoon.

15 recordsLinked to original sources

arXiv2025

Halfway to the Peak: ice absorption bands at $z\approx0.5$ with JWST MIRI/MRS

This paper presents the first combined detections of CO$_2$, CO, XCN and water ices beyond the local Universe. We find gas-phase CO in addition to the solid phase CO. Our source, SSTXFLS J172458.3+591545, is a $z=0.494$ star-forming galaxy which also hosts a deeply obscured AGN. The profiles of its ice features are consistent with those of other Galactic and local galaxy sources and the implied ice mantle composition is similar to that of even more obscured sources. The ice features indicate the presence of a compact nucleus in our galaxy and allow us to place constraints on its density and temperature ($n>10^5$cm$^{-3}$ and $T=20-90K$). We infer the visual extinction towards this nucleus to be $A_V\approx6-7$. An observed plot of $\tau_{Si}$ vs. $\tau_{CO2}/\tau_{Si}$ can be viewed as a probe for both the total dustiness of a system as well as the clumpiness of the dust along the line of sight. This paper highlights the potential of using {\sl JWST} MIRI spectra to study the dust composition and geometric distribution of sources beyond the local Universe.

astro-ph.GA↗

arXiv2022

Discovery of a Dusty, Chemically Mature Companion to a z$\sim$4 Starburst Galaxy in JWST ERS Data

We report the discovery of two companion sources to a strongly lensed galaxy SPT0418-47 ("ring") at redshift 4.225, targeted by the JWST Early Release Science program. We confirm that these sources are at a similar redshift as the ring based on H$\alpha$ detected in the NIRSpec spectrum, and [C II] 158 $\mu$m line from ALMA. Using multiple spectral lines detected in JWST/NIRSpec, the rest-frame optical to infrared images from NIRCam and MIRI, and far-infrared (FIR) dust continuum detected by ALMA, we argue that the newly discovered sources are actually lensed images of the same companion galaxy, hereafter referred to as SPT0418-SE ("SE"), located within 5 kpc in the source plane of the ring. The star formation rate derived using [C II] and dust continuum puts a lower limit of 17 M$_\odot$/yr, while the SFR$_\mathrm{H\alpha}$ is estimated to be >2 times lower, thereby confirming that SE is a heavily dust obscured star-forming galaxy. Analysis using optical strong line diagnostics suggests that SE has near solar elemental abundance, while the ring appears to have super-solar metallicity O/H and N/O. We attempt to reconcile the high metallicity in this system by invoking early onset of star formation with continuous high star forming efficiency, or that optical strong line diagnostics need revision at high redshift. We suggest that SPT0418-47 resides in a massive dark matter halo with yet to be discovered neighbors. This work highlights the importance of joint analysis of JWST and ALMA data for a deep and complete picture of the early Universe.

astro-ph.GA↗

arXiv2022

Stellar and black hole assembly in z<0.3 infrared-luminous mergers: intermittent starbursts vs. super-Eddington accretion

We study stellar and black hole mass assembly in a sample of 42 infrared-luminous galaxy mergers at z<0.3 by combining results from radiative transfer modelling with archival measures of molecular gas and black hole mass. The ratios of stellar mass, molecular gas mass, and black hole mass to each other are consistent with those of massive gas-rich galaxies at z<0.3. The advanced mergers may show increased black hole mass to stellar mass ratios, consistent with the transition from AGN to ellipticals and implying substantial black hole mass growth over the course of the merger. Star formation rates are enhanced relative to the local main sequence, by factors of ~100 in the starburst and ~1.8 in the host. The starburst star formation rates appear distinct to star formation in the main sequence at all redshifts up to at least z~5. Starbursts may prefer late-stage mergers, but are observed at any merger stage. We do not find evidence that the starbursts in these low-redshift systems substantially increase the total stellar mass, with a soft upper limit on the stellar mass increase from starburst activity of about a factor of two. In contrast, 12 objects show evidence for super-Eddington accretion, associated with late-stage mergers, suggesting that many AGN in infrared-luminous mergers go through a super-Eddington phase. The super-Eddington phase may increase black hole mass by up to an order of magnitude at an accretion efficiency of 42+/-33% over a period of 44+/-22Myr. Our results imply that super-Eddington accretion is an important black hole growth channel in infrared-luminous galaxies at all redshifts.

astro-ph.GA↗

arXiv2018

Warm Molecular Hydrogen in Nearby, Luminous Infrared Galaxies

Mid-infrared molecular hydrogen (H$_2$) emission is a powerful cooling agent in galaxy mergers and in radio galaxies; it is a potential key tracer of gas evolution and energy dissipation associated with mergers, star formation, and accretion onto supermassive black holes. We detect mid-IR H$_2$ line emission in at least one rotational transition in 91\% of the 214 Luminous Infrared Galaxies (LIRGs) observed with Spitzer as part of the Great Observatories All-sky LIRG Survey (GOALS). We use H$_2$ excitation diagrams to estimate the range of masses and temperatures of warm molecular gas in these galaxies. We find that LIRGs in which the IR emission originates mostly from the Active Galactic Nuclei (AGN) have about 100K higher H$_2$ mass-averaged excitation temperatures than LIRGs in which the IR emission originates mostly from star formation. Between 10 and 15\% of LIRGs have H$_2$ emission lines that are sufficiently broad to be resolved or partially resolved by the high resolution modules of Spitzer's Infrared Spectrograph (IRS). Those sources tend to be mergers and contain AGN. This suggests that a significant fraction of the H$_2$ line emission is powered by AGN activity through X-rays, cosmic rays, and turbulence. We find a statistically significant correlation between the kinetic energy in the H$_2$ gas and the H$_2$ to IR luminosity ratio. The sources with the largest warm gas kinetic energies are mergers. We speculate that mergers increase the production of bulk in-flows leading to observable broad H$_2$ profiles and possibly denser environments.

astro-ph.GA↗

arXiv2018

The dual role of starburst and active galactic nuclei in driving extreme molecular outflows

We report molecular gas observations of IRAS 20100-4156 and IRAS 03158+4227, two local ultraluminous infrared galaxies (ULIRGs) hosting some of the fastest and most massive molecular outflows known. Using ALMA and PdBI observations, we spatially resolve the CO(1-0) emission from the outflowing molecular gas in both and find maximum outflow velocities of $ v_{\rm max} \sim 1600$ and $\sim 1700$ km/s for IRAS 20100-4156 and IRAS 03158+4227, respectively. We find total gas mass outflow rates of $\dot M_{\rm OF} \sim 670$ and $\sim 350$ Msun/yr, respectively, corresponding to molecular gas depletion timescales $τ^{\rm dep}_{\rm OF} \sim 11$ and $\sim 16$ Myr. This is nearly 3 times shorter than the depletion timescales implied by star formation, $τ^{\rm dep}_{\rm SFR} \sim 33$ and $\sim 46$ Myr, respectively. To determine the outflow driving mechanism, we compare the starburst ($L_{*}$) and AGN ($L_{\rm AGN}$) luminosities to the outflowing energy and momentum fluxes, using mid-infrared spectral decomposition to discern $L_{\rm AGN}$. Comparison to other molecular outflows in ULIRGs reveals that outflow properties correlate similarly with $L_{*}$ and $L_{\rm IR}$ as with $L_{\rm AGN}$, indicating that AGN luminosity alone may not be a good tracer of feedback strength and that a combination of AGN and starburst activity may be driving the most powerful molecular outflows. We also detect the OH 1.667 GHz maser line from both sources and demonstrate its utility in detecting molecular outflows.

astro-ph.GA↗

arXiv2016

HERUS: A CO Atlas from SPIRE Spectroscopy of local ULIRGs

We present the Herschel SPIRE Fourier Transform Spectroscopy (FTS) atlas for a complete flux limited sample of local Ultra-Luminous Infra-Red Galaxies as part of the HERschel ULIRG Survey (HERUS). The data reduction is described in detail and was optimized for faint FTS sources with particular care being taken with the subtraction of the background which dominates the continuum shape of the spectra. Special treatment in the data reduction has been given to any observation suffering from artefacts in the data caused by anomalous instrumental effects to improve the final spectra. Complete spectra are shown covering $200 - 671μ$m with photometry in the SPIRE bands at 250$μ$m, 350$μ$m and 500$μ$m. The spectra include near complete CO ladders for over half of our sample, as well as fine structure lines from [CI] 370 $μ$m, [CI] 609 $μ$m, and [NII] 205 $μ$m. We also detect H$_{2}$O lines in several objects. We construct CO Spectral Line Energy Distributions (SLEDs) for the sample, and compare their slopes with the far-infrared colours and luminosities. We show that the CO SLEDs of ULIRGs can be broadly grouped into three classes based on their excitation. We find that the mid-J (5$<$J$<$8) lines are better correlated with the total far-infrared luminosity, suggesting that the warm gas component is closely linked to recent star-formation. The higher J transitions do not linearly correlate with the far-infrared luminosity, consistent with them originating in hotter, denser gas unconnected to the current star-formation. {\bf We conclude that in most cases more than one temperature components are required to model the CO SLEDs.}

astro-ph.GA↗

arXiv2014

Strong C+ emission in galaxies at z~1-2: Evidence for cold flow accretion powered star formation in the early Universe

We have recently detected the [CII] 157.7 micron line in eight star forming galaxies at redshifts 1 to 2 using the redshift(z) Early Universe Spectrometer (ZEUS). Our sample targets star formation dominant sources detected in PAH emission. This represents a significant addition to [CII] observations during the epoch of peak star formation. We have augmented this survey with observations of the [OI] 63 micron line and far infrared photometry from the PACS and SPIRE Herschel instruments as well as Spitzer IRS spectra from the literature showing PAH features. Our sources exhibit above average gas heating efficiency, many with both [OI]/FIR and [CII]/FIR ~1% or more. The relatively strong [CII] emission is consistent with our sources being dominated by star formation powered PDRs, extending to kpc scales. We suggest that the star formation mode in these systems follows a Schmidt-Kennicutt law similar to local systems, but at a much higher rate due to molecular gas surface densities 10 to 100 times that of local star forming systems. The source of the high molecular gas surface densities may be the infall of neutral gas from the cosmic web. In addition to the high [CII]/FIR values, we also find high [CII]/PAH ratios and, in at least one source, a cool dust temperature. This source, SWIRE 4-5, bears a resemblance in these diagnostics to shocked regions of Stephan's Quintet, suggesting that another mode of [CII] excitation in addition to normal photoelectric heating may be contributing to the observed [CII] line.

astro-ph.GA↗

arXiv2014

Star Formation Rates from [CII] 158 um and Mid Infrared Emission Lines for Starbursts and AGN

A summary is presented for 130 galaxies observed with the Herschel PACS instrument to measure fluxes for the [CII] 158 um emission line. Sources cover a wide range of active galactic nucleus to starburst classifications, as derived from polycyclic aromatic hydrocarbon (PAH) strength measured with the Spitzer Infrared Spectrograph. Redshifts from [CII] and line to continuum strengths (equivalent width of [CII]) are given for the full sample, which includes 18 new [CII] flux measures. Calibration of L([CII)]) as a star formation rate (SFR) indicator is determined by comparing [CII] luminosities with mid-infrared [NeII] and [NeIII] emission line luminosities; this gives the same result as determining SFR using bolometric luminosities of reradiating dust from starbursts: log SFR = log L([CII)]) - 7.0, for SFR in solar masses per year and L([CII]) in solar luminosities. We conclude that L([CII]) can be used to measure SFR in any source to a precision of ~ 50%, even if total source luminosities are dominated by an AGN component. The line to continuum ratio at 158 um, EW([CII]), is not significantly greater for starbursts (median EW([CII]) = 1.0 um) compared to composites and AGN (median EW([CII]) = 0.7 um), showing that the far infrared continuum at 158 um scales with [CII] regardless of classification. This indicates that the continuum at 158 um also arises primarily from the starburst component within any source, giving log SFR = log vLv(158 um) - 42.8 for SFR in solar masses per year and vLv(158 um) in erg per sec.

astro-ph.GA↗

arXiv2013

Far-infrared Fine-Structure Line Diagnostics of Ultraluminous Infrared Galaxies

We present Herschel observations of six fine-structure lines in 25 Ultraluminous Infrared Galaxies at z<0.27. The lines, [O III]52, [N III]57, [O I]63, [N II]122, [O I]145, and [C II]158, are mostly single gaussians with widths <600 km s-1 and luminosities of 10^7 - 10^9 Solar. There are deficits in the [O I]63/L_IR, [N II]/L_IR, [O I]145/L_IR, and [C II]/L_IR ratios compared to lower luminosity systems. The majority of the line deficits are consistent with dustier H II regions, but part of the [C II] deficit may arise from an additional mechanism, plausibly charged dust grains. This is consistent with some of the [C II] originating from PDRs or the ISM. We derive relations between far-IR line luminosities and both IR luminosity and star formation rate. We find that [N II] and both [O I] lines are good tracers of IR luminosity and star formation rate. In contrast, [C II] is a poor tracer of IR luminosity and star formation rate, and does not improve as a tracer of either quantity if the [C II] deficit is accounted for. The continuum luminosity densities also correlate with IR luminosity and star formation rate. We derive ranges for the gas density and ultraviolet radiation intensity of 10^1 < n < 10^2.5 and 10^2.2 < G_0 < 10^3.6, respectively. These ranges depend on optical type, the importance of star formation, and merger stage. We do not find relationships between far-IR line properties and several other parameters; AGN activity, merger stage, mid-IR excitation, and SMBH mass. We conclude that these far-IR lines arise from gas heated by starlight, and that they are not strongly influenced by AGN activity.

astro-ph.CO↗

arXiv2012

Spitzer Observations of Young Red Quasars

We present mid-infrared spectra and photometry of thirteen redshift 0.4<z<1 dust-reddened quasars obtained with Spitzer IRS and MIPS. We compare properties derived from their infrared spectral energy distributions (intrinsic AGN luminosity and far-infrared luminosity from star formation) to the host luminosities and morphologies from HST imaging, and black hole masses estimated from optical and/or near-infrared spectroscopy. Our results are broadly consistent with models in which most dust reddened quasars are an intermediate phase between a merger-driven starburst triggering a completely obscured AGN, and a normal, unreddened quasar. We find that many of our objects have high accretion rates, close to the Eddington limit. These objects tend to fall below the black hole mass -- bulge luminosity relation as defined by local galaxies, whereas most of our low accretion rate objects are slightly above the local relation, as typical for normal quasars at these redshifts. Our observations are therefore most readily interpreted in a scenario in which galaxy stellar mass growth occurs first by about a factor of three in each merger/starburst event, followed sometime later by black hole growth by a similar amount. We do not, however, see any direct evidence for quasar feedback affecting star formation in our objects, for example in the form of a relationship between accretion rate and star formation. Five of our objects, however, do show evidence for outflows in the OIII 5007 Angstrom emission line profile, suggesting that the quasar activity is driving thermal winds in at least some members of our sample.

astro-ph.CO↗

arXiv2011

The radio core of the Ultraluminous Infrared Galaxy F00183-7111: watching the birth of a quasar

F00183-7111 is one of the most extreme Ultra-Luminous Infrared Galaxies known. Here we present a VLBI image which shows that F00183-7111 is powered by a combination of a radio-loud Active Galactic Nucleus surrounded by vigorous starburst activity. Although already radio-loud, the quasar jets are only 1.7 kpc long, boring through the dense gas and starburst activity that confine them. We appear to be witnessing this remarkable source in the brief transition period between merging starburst and radio-loud "quasar-mode" accretion.

astro-ph.CO↗

arXiv2010

Principal component analysis of the Spitzer IRS spectra of ultraluminous infrared galaxies

We present the first principal component analysis (PCA) applied to a sample of 119 Spitzer Infrared Spectrograph (IRS) spectra of local ultraluminous infrared galaxies (ULIRGs) at z<0.35. The purpose of this study is to objectively and uniquely characterise the local ULIRG population using all information contained in the observed spectra. We have derived the first three principal components (PCs) from the covariance matrix of our dataset which account for over 90% of the variance. The first PC is characterised by dust temperatures and the geometry of the mix of source and dust. The second PC is a pure star formation component. The third PC represents an anti-correlation between star formation activity and a rising AGN. Using the first three PCs, we are able to accurately reconstruct most of the spectra in our sample. Our work shows that there are several factors that are important in characterising the ULIRG population, dust temperature, geometry, star formation intensity, AGN contribution, etc. We also make comparison between PCA and other diagnostics such as ratio of the 6.2 microns PAH emission feature to the 9.7 micron silicate absorption depth and other observables such as optical spectral type.

astro-ph.CO↗

arXiv2007

Spitzer Mid-Infrared Spectroscopy of Infrared Luminous Galaxies at z~2 II: Diagnostics

We present mid-IR spectral decomposition of a sample of 48 Spitzer-selected ULIRGs spanning z~1-3 and likely L_IR~10^12-10^13Lsun. Our study aims at quantifying the star-formation and AGN processes in these sources which recent results suggest have evolved strongly between the observed epoch and today. To do this, we study the mid-IR contribution of PAH emission, continuum, and extinction. About 3/4 of our sample are continuum- (i.e. AGN) dominated sources, but ~60% of these show PAH emission, suggesting the presence of star-formation activity. These sources have redder mid-IR colors than typical optically-selected quasars. About 25% of our sample have strong PAH emission, but none are likely to be pure starbursts as reflected in their relatively high 5um hot dust continua. However, their steep 30um-to-14um slopes suggest that star-formation might dominate the total infrared luminosity. Six of our z~2 sources have EW6.2>~0.3um and L_14um>~10^12Lsun (implying L_IR>~10^13Lsun). At these luminosities, such high EW6.2 ULIRGs do not exist in the local Universe. We find a median optical depth at 9.7um of =1.4. This is consistent with local IRAS-selected ULIRGs, but differs from early results on SCUBA-selected z~2 ULIRGs. Similar to local ULIRGs about 25% of our sample show extreme obscuration (tau_9.7>~3) suggesting buried nuclei. In general, we find that our sources are similar to local ULIRGs, but are an order of magnitude more luminous. It is not clear whether our z~2 ULIRGs are simply scaled-up versions of local ULIRGs, or subject to fundamentally different physical processes.

astro-ph↗

arXiv2004

Spitzer-IRS mapping of the inner kpc of NGC 253: Spatial distribution of the Ne III, PAH 11.3 microns and H2 (0-0) S(1) lines and a gradient in the Ne III/Ne II line ratio

We present our early results of the mapping of the nucleus of the starburst galaxy NGC 253 and its immediate surroundings using the Infrared Spectrograph onboard the Spitzer Space Telescope. The map is centered on the nucleus of the galaxy and spans the inner 800 x 688 pc2. The spatial distribution of the \neiii line at 15.55 microns and the polycyclic aromatic hydrocarbons feature at 11.3 microns peaks at the center while the purely rotationnal transition of molecular hydrogen at 17.03 microns is strong over several slit positions. We perform a brief investigation of the implications of these measurement on the properties of the star formation in this region using theories developped to explain the deficiency of massive stars in starbursts.

astro-ph↗

arXiv2003

ISO observations of four active galaxies

We present ISO PHOT-S spectra of four galaxies known or suspected to host a central AGN, selected from the initial Iras/Rosat sample of Boller et al. (1992). Two of them had no obvious Seyfert features in their previous optical spectra: IRAS 14201+2956, and IRAS 21582+1018. The latter was bright enough to also allow SWS observations around selected neon lines, to establish its excitation. While both PHOT-S spectra are characteristic of starburst-dominated galaxies, the neon line ratios in IRAS 21582+1018 indicate the presence of a hard excitation source. New, high-resolution, optical spectra show only a weak, broad component around Halpha, classifying now these two objects as Sey 1.9 galaxies. The two other galaxies observed are the NLS1 galaxies Mrk 359 and Mrk 1388. Their ISO spectra however do not reveal the typical, strong PAH features found in the starburst galaxies and are more like those of standard Seyferts. These results show therefore that, although IR observations were expected to be able to always reveal the presence of an active nucleus by piercing through the central obscuration, the result may be ambiguous: the broad band IR energy distribution can still be dominated by starburts located in a circumnuclear region, and the AGN appear only in specific observations (high-excitation lines in the IR, or optical spectra with better quality than classification spectra). The obscuration needs however to be patchy rather than complete, to explain the detection of the high-excitation lines or broad Balmer wings. Only high-energy observations can then establish the strength of the central AGN and the amount of extinction with certainty.

astro-ph↗