The properties of the interstellar medium of galaxies across time as traced by the neutral atomic carbon [CI]
Francesco Valentino, Georgios E. Magdis, Emanuele Daddi, Daizhong Liu, Manuel Aravena, Frederic Bournaud, Isabella Cortzen, Yu Gao, Shuowen Jin, Stephanie Junea… 展开作者
Francesco Valentino, Georgios E. Magdis, Emanuele Daddi, Daizhong Liu, Manuel Aravena, Frederic Bournaud, Isabella Cortzen, Yu Gao, Shuowen Jin, Stephanie Juneau, Jeyhan S. Kartaltepe, Vasily Kokorev, Min-Young Lee, Suzanne C. Madden, Desika Narayanan, Gergo Popping, Annagrazia Puglisi
备注：
20 pages + Appendix, accepted for publication in the Astrophysical Journal on Dec. 20th, 2019. The data compilation is available in the online version of the article
We report ALMA observations of the neutral atomic carbon transitions [CI] and multiple CO lines in a sample of $\sim30$ main sequence galaxies at $z\sim1$, including novel information on [CI](2-1) and CO(7-6) for 7 of such normal objects. We complement our observations with a collection of $>200$ galaxies with coverage of similar transitions, spanning the $z=0-4$ redshift interval and a variety of ambient conditions from local to high-redshift starbursts. We find systematic variations in the [CI]/IR and [CI]/high-$J$ ($J=7$) CO luminosity ratios among the various samples. We interpret these differences as increased dense molecular gas fractions and star formation efficiencies in the strongest high-redshift starbursts with respect to normal main sequence galaxies. We further report constant $L'_{\rm [CI]2-1}$/$L'_{\rm [CI]1-0}$ ratios across the galaxy populations and redshifts, suggesting that gas temperatures $T_{\rm exc}$ traced by [CI] do not strongly vary. We find only a mild correlation with $T_{\rm dust}$ and that, generally, $T_{\rm exc} \lesssim T_{\rm dust}$. We fit the line ratios with classical PDR models, retrieving consistently larger densities and intensities of the UV radiation fields in submm galaxies than in main sequence and local objects. However, these simple models fall short in representing the complexity of a multiphase interstellar medium and should be treated with caution. Finally, we compare our observations with the Santa Cruz semi-analytical model of galaxy evolution, recently extended to simulate submm emission. While we confirm the success in reproducing the CO lines, we find systematically larger [CI] luminosities at fixed IR luminosity than predicted theoretically. This highlights the necessity of improving our understanding of the mechanisms regulating the [CI] emission on galactic scales. We release our data compilation to the community.
Context. Hydrogenated amorphous carbons, a-C:H, can incorporate a variety of heteroatoms, which can lead to interesting effects. Aims. To investigate the doping of interstellar a-C:H grains with, principally, Si, O, N and S atoms within the astrophysical context. Methods. A search of the literature on doped a-C:H reveals a number of interesting phenomena of relevance to astrophysics. Results. X dopants in a-C:H:X materials can affect the sp3/sp2 ratio (X = Si, O and N), lead to blue photoluminescence (undoped or X = N), induce ferromagnetic-like behaviour (X = N and S) or simply be incorporate…
The 29 reactions linking carbon monosulfide (CS) to methyl mercaptan (CH3SH) via ten intermediate radicals and molecules have been characterized with relevance to surface chemistry in cold interstellar ices. More intermediate species than previously considered are found likely to be present in these ices, such as trans- and cis-HCSH. Both activation and reaction energies have been calculated, along with low-temperature (T > 45~K) rate constants for the radical-neutral reactions. For barrierless radical-radical reactions on the other hand, branching ratios have been determined. The combination …
The interstellar medium contains dust and gas, in which at high densities and cold conditions molecules can proliferate. Interstellar Complex Organic Molecules (iCOMs) are C-bearing species that contain at least six atoms. As they are detected in young stellar objects, iCOMs are expected to inhabit the early stages of the star formation evolution. In this study, we try to determine which iCOMs are present in the outflow component of massive protostars. To do this, we analyzed the morphological extension of blue- and red-shifted iCOMs emission in a sample of eleven massive protostars employing …
The present study provides an investigation on the deposition of carbon-related products on different substrates using a high power dielectric barrier discharge fed with helium and saturated hydrocarbon gases. The discharge has been characterized by means of voltage-current measurements, while the neutral species and the dissociation compounds accumulated in the plasma reactor have been analyzed by Fourier-transform infrared (FTIR) spectroscopy. The properties of non-aromatic hydrogenated amorphous carbon (a-C:H) films and 'fluffy' carbon dust deposited onto various substrates are analyzed by …
In the second paper of the series, we have modeled low frequency carbon radio recombination lines (CRRL) from the interstellar medium. Anticipating the LOw Frequency ARray (LOFAR) survey of Galactic CRRLs, we focus our study on the physical conditions of the diffuse cold neutral medium (CNM). We have used the improved departure coefficients computed in the first paper of the series to calculate line-to-continuum ratios. The results show that the line width and integrated optical depths of CRRL are sensitive probes of the electron density, gas temperature, and the emission measure of the cloud.…
This review summarises what we have learnt in the last two decades based on HI 21-cm absorption observations about the cold interstellar medium (ISM) in the central regions of active galaxies and the interplay between this gas and the active nucleus (AGN). HI absorption is a powerful tracer on all scales, from the pc scales to many tens of kpc. Given the strong radio continuum often associated with the central activity, HI absorption can be used to study the HI near an AGN out to much higher redshifts than is possible using HI emission. HI absorption has been used to characterise the general I…
We present an analysis of the kinematic properties of stellar populations in the Galactic halo, making use of over 100,000 main sequence turnoff (MSTO) stars observed in the Sloan Digital Sky Survey. After dividing the Galactic halo into an inner-halo region (IHR) and outer-halo region (OHR), based on the spatial variation of carbon-to-iron ratios in the sample, we find that stars in the OHR exhibit a clear retrograde motion of $-$49 $\pm$ 4 km s$^{-1}$ and a more spherical distribution of stellar orbits, while stars in the IHR have zero net rotation ($-$3 $\pm$ 1 km s$^{-1}$) with a much more…
Since their discovery in 1991, carbon nanotubes (CNTs) -- a novel one-dimensional carbon allotrope -- have attracted considerable interest worldwide because of their potential technological applications such as electric and optical devices. In the astrophysical context, CNTs may be present in the interstellar space since many of the other allotropes of carbon (e.g., amorphous carbon, fullerenes, nanodiamonds, graphite, polycyclic aromatic hydrocarbons, and possibly graphene as well) are known to be widespread in the Universe, as revealed by presolar grains in carbonaceous primitive meteorites …
Carbon macromolecules are intermediates between small gas-phase species and larger dust structures. I illustrate how observations and dedicated laboratory experiments support this picture.
We analyse the far-infrared properties of $\sim$ 5,000 star-forming galaxies at $z<4.5$, drawn from the deepest, super-deblended catalogues in the GOODS-N and COSMOS fields. We develop a novel panchromatic SED fitting algorithm, $\texttt{Stardust}$, that models the emission from stars, AGN, and infrared dust emission, without relying on energy balance assumptions. Our code provides robust estimates of the UV-optical and FIR physical parameters, such as the stellar mass ($M_*$), dust mass ($M_{\rm dust}$), infrared luminosities ($L_{\rm IR}$) arising from AGN and star formation activity, and th…
Molecular hydrogen clouds are a key component of the interstellar medium because they are the birthplaces for stars. They are embedded in atomic gas that pervades the interstellar space. However, the details of how molecular clouds assemble from and interact with the atomic gas are still largely unknown. As a result of new observations of the 158~$μ$m line of ionized carbon CII in the Cygnus region within the FEEDBACK program on SOFIA (Stratospheric Observatory for Infrared Astronomy), we present compelling evidence that CII unveils dynamic interactions between cloud ensembles. This process is…
CO-dark molecular gas traced by HCO$^+$ in the diffuse interstellar medium
University of Wisconsin–Madison（威斯康星大学麦迪逊分校）；National Radio Astronomy Observatory（美国国家射电天文台）；Macquarie University（麦考瑞大学）；CSIRO Space & Astronomy（澳大利亚联邦科学与工业研究组织空间与天文部）；Korea Astronomy and Space Science Institute（韩国天文学与空间科学研究所）；University of Science and Technology（科学技术大学）；Institut de Radioastronomie Millimetrique（毫米波射电天文研究所）
We study conditions under which carbon clusters of different sizes form and stabilize. {We describe an approach to equilibrium by simulating tenuous carbon gas dynamics to long times.} First, we use reactive molecular dynamics simulations to describe the nucleation of long chains, large clusters, and complex cage structures in carbon and hydrogen rich interstellar gas phases. We study how temperature, particle density, presence of hydrogen, and carbon inflow affect the nucleation of molecular moieties with different characteristics, in accordance with astrophysical conditions. We extend the si…
Observational evidence seems to indicate that the depletion of interstellar carbon into dust shows rather wide variations and that carbon undergoes rather rapid recycling in the interstellar medium (ISM). Small hydrocarbon grains are processed in photo-dissociation regions by UV photons, by ion and electron collisions in interstellar shock waves and by cosmic rays. A significant fraction of hydrocarbon dust must therefore be re-formed by accretion in the dense, molecular ISM. A new dust model (Jones et al., Astron. Astrophys., 2013, 558, A62) shows that variations in the dust observables in th…
In an effort to further our interest in understanding basic chemistry of interstellar molecules, we carry out here an extensive investigation of the stabilities of interstellar carbon chains; Cn, H2Cn, HCnN and CnX (X=N, O, Si, S, H, P, H-, N-). These sets of molecules accounts for about 20% of all the known interstellar and circumstellar molecules, their high abundances therefore demand a serious attention. High level ab initio quantum chemical calculations are employed to accurately estimate enthalpy of formation, chemical reactivity indices; global hardness and softness; and other chemical …
We report a systematic study of all known methyl carbon chains toward TMC-1 using the second data release of the GOTHAM survey, as well as a search for larger species. Using Markov-Chain Monte Carlo simulations and spectral line stacking of over 30 rotational transitions, we report statistically significant emission from methylcyanotriacetylene (CH$_3$C$_7$N) at a confidence level of 4.6$σ$, and use it to derive a column density of ${\sim}$10$^{11}$ cm$^{-2}$. We also searched for the related species, methyltetraacetylene (CH$_3$C$_8$H), and place upper limits on the column density of this mol…
Using atomistic simulations, we characterize the adsorption process of organic molecules on carbon nanoparticles, both of which have been reported to be abundant in the interstellar medium (ISM). It is found that the aromatic organics are adsorbed more readily than the aliphatic ones. This selectivity would favor the formation of polycyclic aromatic hydrocarbons (PAHs) or fullerene-like structures in the ISM due to structural similarity. It is also observed in our simulations that the molecules form a monolayer over the nanoparticle surface before stacking up in aggregates. This suggests a pos…
Some observations of warm carbon chain chemistry (WCCC) cores indicate that they are often located near the edges of molecular clouds. This finding may suggest that WCCC is promoted in star-forming cores exposed to radiation from the interstellar medium. We aim to investigate the chemistry of carbon chains in such a core. A chemical simulation of a gas parcel in a low-mass star-forming core with a full level of irradiation by interstellar photons and cosmic rays was compared to a simulation of a core receiving only one-tenth of such irradiation. In the full irradiation model, the abundances of…
In the interstellar medium, carbon is distributed between the gas and solid phases. However, while about half of the expected carbon abundance can be accounted for in the gas phase, there is considerable uncertainty as to the amount incorporated in interstellar dust. The aliphatic component of the carbonaceous dust is of particular interest because it produces a significant 3.4 $μ$m absorption feature when viewed against a background radiation source. The optical depth of the 3.4 $μ$m absorption feature is related to the number of aliphatic carbon C-H bonds along the line of sight. It is possi…
How dust scatters and absorbs starlight in the interstellar medium (ISM) contains important clues about the size and composition of interstellar dust. While the ultraviolet (UV) and visible interstellar extinction is well studied and can be closely fitted in terms of various dust mixtures (e.g., the silicategraphite mixture), the infrared (IR) extinction is not well understood, particularly, the mid-IR extinction in the 3-8 micron wavelength range is rather flat (or "gray") and is inconsistent with the standard Mathis, Rumpl, & Nordsieck (MRN) silicate-graphite dust model. We attempt to reprod…
The largest non-cyclic molecules detected in the interstellar medium (ISM) are organic with a straight-chain carbon backbone. We report an interstellar detection of a branched alkyl molecule, iso-propyl cyanide (i-C3H7CN), with an abundance 0.4 times that of its straight-chain structural isomer. This detection suggests that branched carbon-chain molecules may be generally abundant in the ISM. Our astrochemical model indicates that both isomers are produced within or upon dust grain ice mantles through the addition of molecular radicals, albeit via differing reaction pathways. The production of…
The design, implementation, and performance of a customized carbon atom beam source for the purpose of investigating solid-state reaction routes in interstellar ices in molecular clouds are discussed. The source is integrated into an existing ultrahigh vacuum setup, SURFace REaction SImulation DEvice (SURFRESIDE$^{2}$), which extends this double atom (H/D, O, and N) beamline apparatus with a third atom (C) beamline to a unique system that is fully suited to explore complex organic molecule solid-state formation under representative interstellar cloud conditions. The parameter space for this sy…
Cosmic Rays (CR) process the matter of the Interstellar Medium. Such energetic processing not only modifies the interstellar matter but also injects chemical species in the gas phase. In this work, we study the effect of the CR on the astrophysical polycyclic aromatic hydrocarbons (PAH). For events in which many electrons are stripped out from the PAH by interaction with a heavy cosmic ray particle, coulomb explosion takes place and carbon chains are produced. The fragments production rates of carbon chains are of particular interest for astrophysical models. We computed PAH multi-ionization c…
The distribution of various interstellar gas components and the pressure in the interstellar medium (ISM) is a result of the interplay of different dynamical mechanisms and energy sources on the gas in the Milky Way. The scale heights of the different gas tracers, such as HI and CO, are a measure of these processes. The scale height of [CII] emission in the Galactic plane is important for understanding those ISM components not traced by CO or HI. We determine the average distribution of [CII] perpendicular to the plane in the inner Galactic disk and compare it to the distributions of other key…
Long-chain hydrocarbon anions CnH- (n=4, 6, 8) have recently been found to be abundant in a variety of interstellar clouds. In order to explain their large abundances in the denser (prestellar/protostellar) environments, new chemical models are constructed that include gas-grain interactions. Models including accretion of gas-phase species onto dust grains and cosmic-ray-induced desorption of atoms are able to reproduce the observed anion-to-neutral ratios, as well as the absolute abundances of anionic and neutral carbon chains, with a reasonable degree of accuracy. Due to their destructive ef…
The motion of diamagnetic dust particles in interstellar magnetic fields is studied numerically with several different sets of parameters. Two types of behavior are observed, depending on the value of the critical number $R$, which is a function of the grain inertia, the magnetic susceptibility of the material and of the strength of rotation braking. If $R\leq10$, the grain ends up in a static state and perfectly aligned with the magnetic field, after a few braking times. If not, it goes on precessing and nutating about the field vector for a much longer time. Usual parameters are such that th…
Chemical Evolution during Molecular Cloud Formation Triggered by an Interstellar Shock Wave: Dependence on Shock Parameters and Comparison with Molecular Absorption Lines
We report the detection of microwave emission lines from the hydrocarbon anion C6H- and its parent neutral C6H in the star-forming region L1251A (in Cepheus), and the pre-stellar core L1512 (in Auriga). The carbon-chain-bearing species C4H, HC3N, HC5N, HC7N and C3S are also detected in large abundances. The observations of L1251A constitute the first detections of anions and long-chain polyynes and cyanopolyynes (with more than 5 carbon atoms) in the Cepheus Flare star-forming region, and the first detection of anions in the vicinity of a protostar outside of the Taurus molecular cloud complex…
Carbon monoxide (CO) is the second most abundant molecule in the gas-phase of the interstellar medium. In dense molecular clouds, it is also present in the solid-phase as a constituent of the mixed water-dominated ices covering dust grains. Its presence in the solid-phase is inferred from its infrared (IR) signals. In experimental observations of solid CO/water mixed samples, its IR frequency splits into two components, giving rise to a blue- and a redshifted band. However, in astronomical observations, the former has never been observed. Several attempts have been carried out to explain this …
By applying quantum chemical calculation, interstellar infrared spectrum was categorized to three classes. Type-A show unusual feature of strong peaks at 11.3,12.9, and 14.0 micrometer. Usually observed 6.2, 7.7, and 8.6 micrometer bands are weak or not recognized. Typical examples are NGC1316 and NGC4589. Such spectrum could be identified for the first time by pure carbon molecule (C23)2+ (dication) having two carbon pentagons combined with five hexagons. Calculated spectrum coincided well at 11.3, 13.0, and 14.0 micrometer. Also we could find more coincidence at 5.2, 5.6, 7.6, 8.8,10.6,15.7 …
Surface chemistry on cosmic dust grains plays an important role in the formation of molecules at low temperatures in the interstellar and circumstellar environments. For the first time, we experimentally put in evidence the catalytic role of dust surfaces using the thermal reaction CO2 + 2NH3 = NH4+NH2COO-, which is also a proxy of radical-radical reactions. Nanometre-sized amorphous silicate and carbon grains produced in our laboratory were used as grain analogues. Surface catalysis on grains accelerates the kinetics of the reaction studied at a temperature of 80 K by a factor of up to 3 comp…
The high interstellar abundances of polycyclic aromatic hydrocarbons (PAHs) and their size distribution are the result of complex chemical processes implying dust, UV radiation, and the main gaseous components (H, C+, and O). These processes must explain the high abundance of relatively small PAHs in the diffuse interstellar medium (ISM) and imply the continuous formation of some PAHs that are small enough (number of carbon atoms NC <~ 35-50) to be completely dehydrogenated by interstellar UV radiation. The carbon clusters Cn thus formed are constantly exposed to the absorption of ~10-13.6 eV …
We present a study on the prospects of observing carbon, sulfur, and other lower abundance elements (namely Al, Ca, Ti and Ni) present in the interstellar medium using future X-ray instruments. We focus in particular on the detection and characterization of interstellar dust along the lines of sight. We compare the simulated data with different sets of dust aggregates, either obtained from past literature or measured by us using the SOLEIL-LUCIA synchrotron beamline. Extinction by interstellar grains induces modulations of a given photolelectric edge, which can be in principle traced back to t…
In the interstellar medium, the cosmic elemental carbon abundance includes the total carbon in both gas and solid phases. The aim of the study was to trial a new method for measuring the amount and distribution of aliphatic carbon within interstellar dust over wide fields of view of our Galaxy. This method is based on measurement of the 3.4 $μ$m absorption feature from aliphatic carbonaceous matter. This can readily be achieved for single sources using IR spectrometers. However, making such measurements over wide fields requires an imaging IR camera, equipped with narrow-band filters that are …
Molecular cloud dispersal traced by the ionized carbon 158 micron line
I. Physikalisches Institut, Universität zu Köln（科隆大学第一物理研究所）；Green Bank Observatory（格林班克天文台）；University of Maryland, Department of Astronomy（马里兰大学天文学系）；Leiden Observatory（莱顿天文台）；SOFIA Science Center, USRA, NASA Ames Research Center（NASA阿姆斯研究中心USRA SOFIA科学中心）；Astronomisches Rechen-Institut, ZfA Universität Heidelberg（海德堡大学ZfA天体计算研究所）；Center for Gravitational Waves and Cosmology, West Virginia University（西弗吉尼亚大学引力波与宇宙学中心）
The origin of the diffuse interstellar bands is one of the longest-standing mysteries of the interstellar medium is explored within the framework of The Heterogeneous dust Evolution Model at the IaS (THEMIS). The likely nature of the diffuse interstellar band carriers and their evolution is here explored within the framework of the structures and sub-structures inherent to doped hydrogenated amorphous carbon grains in the interstellar medium. Based on the natural aromatic-rich moieties (ashphaltenes) recovered from coal and oil the likely structure of their interstellar analogues is investigat…
CONTEXT: [ABRIDGED]. For the Milky Way bulge, there are currently essentially no measurements of carbon in un-evolved stars, hampering our abilities to properly compare Galactic chemical evolution models to observational data for this still enigmatic stellar population. AIMS: We aim to determine carbon abundances for our sample of 91 microlensed bulge dwarf and subgiant stars. Together with new determinations for oxygen this forms the first statistically significant sample of bulge stars that have C and O abundances measured, and for which the C abundances have not been altered by the nuclear …
2MASS Two-Color Interstellar Reddening Lines in the Inner Galaxy
测定了内银河系（从狐狸座到半人马座）26个区域的2 MASS J-H-H-Ks图中星际红化线的斜率。在大多数研究方向上，E（J-H）/E（H-K_s）的比值在1.9和2.0之间，视消光小于12等的恒星，消光较大的恒星向下偏离红化较弱的恒星的红化线。这可能与带宽效应引起的红化线的曲率有关。然而，一些偏离的恒星可能是严重变红的富氧和富碳AGB星（最新M子类或N型碳星的巨星），以及前主序星（YSO）。
The dust extinction curves toward individual sight lines in M33 are derived for the first time with a sample of reddened O-type and B-type supergiants obtained from the LGGS. The observed photometric data are obtained from the LGGS, PS1 Survey, UKIRT, PHATTER Survey, GALEX, Swift/UVOT and XMM-SUSS. We combine the intrinsic spectral energy distributions (SEDs) obtained from the ATLAS9 and Tlusty stellar model atmosphere extinguished by the model extinction curves from the silicate-graphite dust model to construct model SEDs. The extinction traces are distributed along the arms in M33, and the d…
Laboratory spectra of hydrogenated amorphous carbon (HAC) particles prepared under a variety of conditions show spectral features at 7.05, 8.5, 17.4 and 18.9 μm (1418, 1176, 575 & 529 cm-1) that have been associated with emission from C60 molecules. These lines occur in the spectra even though C60 molecules as such are not present in our samples. It appears that these four spectral lines in HAC can instead be associated with precursor molecules or "proto-fullerenes" that subsequently react to yield C60. We develop a model tracing the evolution and de-hydrogenation of HAC dust and show that the…
We present a study exploring the nature and properties of the Circum-Galactic Medium (CGM) and its connection to the atomic gas content in the interstellar medium (ISM) of galaxies as traced by the HI 21cm line. Our sample includes 45 low-z (0.026-0.049) galaxies from the GALEX Arecibo SDSS Survey. Their CGM was probed via absorption in the spectra of background Quasi-Stellar Objects at impact parameters of 63 to 231kpc. The spectra were obtained with the Cosmic Origins Spectrograph aboard the Hubble Space Telescope. We detected neutral hydrogen (Ly$α$ absorption-lines) in the CGM of 92% of th…
In the interstellar medium, carbon (nano-)grains are a major component of interstellar dust. This solid phase is more vulnerable to processing and destruction than its silicate counterpart. It exhibits a complex, size-dependent evolution due to interactions within different radiative and dynamical environments. Infrared signatures of these nanocarbon grains are seen in a large number of disks around Herbig HAeBe stars. We probe the composition and evolution of carbon nano-grains at the surface of (pre-)transitional protoplanetary disks around Herbig stars. We present spatially resolved infrare…
Modeling a promising carrier of the astronomically observed polycyclic aromatic hydrocarbon (PAH), infrared (IR) spectra of ionized molecules (C9H7) n+ were calculated based on density functional theory (DFT). In a previous study, it was found that void induced coronene C23H12++ could reproduce observed spectra from 3 to 15 micron, which has carbon two pentagons connected with five hexagons. In this paper, we tried to test the simplest model, that is, one pentagon connected with one hexagon, which is indene like molecule (C9H7) n+ (n=0 to 4). DFT based harmonic frequency analysis resulted that…
We probe the role of carbon in the ultraviolet (UV) extinction by examining the relations between the amount of carbon required to be locked up in dust [C/H]_dust with the 2175 Angstrom extinction bump and the far-UV extinction rise, based on an analysis of the extinction curves along 16 Galactic sightlines for which the gas-phase carbon abundance is known and the 2175 Angstrom extinction bump exhibits variable strengths and widths. We derive [C/H]_dust from the Kramers-Kronig relation which relates the wavelength-integrated extinction to the total dust volume. This approach is less model-depe…
Buckminsterfullerene, C60 , is the largest molecule observed to date in interstellar and circumstellar environments. The mechanism of formation of this molecule is actively debated. Despite targeted searches in primitive carbonaceous chondrites, no unambiguous detection of C60 in a meteorite has been reported to date. Here we report the first firm detection of fullerenes, from C30 to at least C100 , in the Almahata Sitta (AhS) polymict ureilite meteorite. This detection was achieved using highly sensitive laser desorption laser ionization mass spectrometry. Fullerenes have been unambiguously d…
The identification of the carriers of the diffuse interstellar bands (DIBs) remains to be established, with the exception of five bands attributed to C60+, although it is generally agreed that DIB carriers should be large carbon-based molecules (with ~10-100 atoms) in the gas phase, such as polycyclic aromatic hydrocarbons (PAHs), long carbon chains or fullerenes. More specific possible carriers among PAHs are investigated, namely elongated molecules, which could explain a correlation between the DIB wavelength and the apparent UV resilience of their carriers. We address the case of polyacenes…
