arXiv subjects
Publications and source records attributed to Dimitra Rigopoulou.
We report the detection of ADFS-27, a dusty, starbursting major merger at a redshift of z=5.655, using the Atacama Large Millimeter/submillimeter Array (ALMA). ADFS-27 was selected from Herschel/SPIRE and APEX/LABOCA data as an extremely red "870 micron riser" (i.e., S_250 ~3.
The [CII] 158um fine-structure line is the brightest emission line observed in local star-forming galaxies. As a major coolant of the gas-phase interstellar medium, [CII] balances the heating, including that due to far-ultraviolet photons, which heat the gas via the photoelectric effect. However, the origin of [CII] emission remains unclear, because C+ can be found in multiple phases of the interstellar medium. Here we measure the fractions of [CII] emission originating in the ionized and neutral gas phases of a sample of nearby galaxies. We use the [NII] 205um fine-structure line to trace the ionized medium, thereby eliminating the strong density dependence that exists in the ratio of [CII]/[NII] 122um. Using the FIR [CII] and [NII] emission detected by the KINGFISH and Beyond the Peak Herschel programs, we show that 60-80% of [CII] emission originates from neutral gas. We find that the fraction of [CII] originating in the neutral medium has a weak dependence on dust temperature and the surface density of star formation, and a stronger dependence on the gas-phase metallicity. In metal-rich environments, the relatively cooler ionized gas makes substantially larger contributions to total [CII] emission than at low abundance, contrary to prior expectations. Approximate calibrations of this metallicity trend are provided.
We present the results from Atacama Large Millimeter/submillimeter Array (ALMA) imaging in the [NII] 205 micron fine-structure line (hereafter [NII]) and the underlying continuum of BRI 1202-0725, an interacting galaxy system at $z =$ 4.7, consisting of an optical QSO, a sub-millimeter galaxy (SMG) and two Lyman-$α$ emitters (LAEs), all within $\sim$25 kpc of the QSO. We detect the QSO and SMG in both [NII] and continuum. At the $\sim$$1"$ (or 6.6 kpc) resolution, both QSO and SMG are resolved in [NII], with the de-convolved major axes of $\sim$9 and $\sim$14 kpc, respectively. In contrast, their continuum emissions are much more compact and unresolved even at an enhanced resolution of $\sim$$0.7"$. The ratio of the [NII] flux to the existing CO (7$-$6) flux is used to constrain the dust temperature ($T_{\rm dust}$) for a more accurate determination of the FIR luminosity $L_{\rm FIR}$. Our best estimated $T_{\rm dust}$ equals $43 (\pm 2)$ K for both galaxies (assuming an emissivity index $β= 1.8$). The resulting $L_{\rm CO(7-6)}/L_{\rm FIR}$ ratios are statistically consistent with that of local luminous infrared galaxies, confirming that $L_{\rm CO(7-6)}$ traces the star formation (SF) rate (SFR) in these galaxies. We estimate that the on-going SF of the QSO (SMG) has a SFR of 5.1 $(6.9) \times 10^3 M_{\odot}$ yr$^{-1}$ ($\pm$ 30%) assuming Chabrier initial mass function, takes place within a diameter (at half maximum) of 1.3 (1.5) kpc, and shall consume the existing 5 $(5) \times 10^{11} M_{\odot}$ of molecular gas in 10 $(7) \times 10^7$ years.
Submillimeter galaxies (SMGs) at $z\gtrsim1$ are luminous in the far-infrared and have star-formation rates, SFR, of hundreds to thousands of solar masses per year. However, it is unclear whether they are true analogs of local ULIRGs or whether the mode of their star formation is more similar to that in local disk galaxies. We target these questions by using Herschel-PACS to examine the conditions in the interstellar medium (ISM) in far-infrared luminous SMGs at z~1-4. We present 70-160 micron photometry and spectroscopy of the [OIV]26 micron, [FeII]26 micron, [SIII]33 micron, [SiII]34 micron, [OIII]52 micron, [NIII]57 micron, and [OI]63 micron fine-structure lines and the S(0) and S(1) hydrogen rotational lines in 13 lensed SMGs identified by their brightness in early Herschel data. Most of the 13 targets are not individually spectroscopically detected and we instead focus on stacking these spectra with observations of an additional 32 SMGs from the \herschel\ archive -- representing a complete compilation of PACS spectroscopy of SMGs. We detect [OI]63 micron, [SiII]34 micron, and [NIII]57 micron at >3sigma in the stacked spectra, determining that the average strengths of these lines relative to the far-IR continuum are $(0.36\pm0.12)\times10^{-3}$, $(0.84\pm0.17)\times10^{-3}$, and $(0.27\pm0.10)\times10^{-3}$, respectively. Using the [OIII]52/[NIII]57 emission line ratio we show that SMGs have average gas-phase metallicities $\gtrsim Z_{\rm sun}$. By using PDR modelling and combining the new spectral measurements with integrated far-infrared fluxes and existing [CII]158 micron data we show that SMGs have average gas densities, n, of $\sim10^{1-3}{\rm cm^{-3}}$ and FUV field strengths, $G_0\sim10^{2.2-4.5}$ (in Habing units: $1.6\times10^{-3}{\rm erg~cm^{-2}~s^{-1}}$), consistent with both local ULIRGs and lower luminosity star-forming galaxies.
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$<$8) lines are better correlated with the total far-infrared luminosity, suggesting that the warm gas component is closely linked to recent star-formation. The higher J transitions do not linearly correlate with the far-infrared luminosity, consistent with them originating in hotter, denser gas unconnected to the current star-formation. {\bf We conclude that in most cases more than one temperature components are required to model the CO SLEDs.}
We use 3035 Herschel-SPIRE 500$μ$m sources from 20.3 sq deg of sky in the HerMES Lockman, ES1 and XMM-LSS areas to estimate the star-formation rate density at z = 1-6. 500 mu sources are associated first with 350 and 250 mu sources, and then with Spitzer 24 mu sources from the SWIRE photometric redshift catalogue. The infrared and submillimetre data are fitted with a set of radiative-transfer templates corresponding to cirrus (quiescent) and starburst galaxies. Lensing candidates are removed via a set of colour-colour and colour-redshift constraints. Star-formation rates are found to extend from < 1 to 20,000 Mo/yr. Such high values were also seen in the all-sky IRAS Faint Source Survey. Star-formation rate functions are derived in a series of redshift bins from 0-6, combined with earlier far-infrared estimates, where available, and fitted with a Saunders et al (1990) functional form. The star-formation-rate density as a function of redshift is derived and compared with other estimates. There is reasonable agreement with both infrared and ultraviolet estimates for z < 3, but we find higher star-formation-rate densities than ultraviolet estimates at z = 3-6. Given the considerable uncertainties in the submillimetre estimates, we can not rule out the possibility that the ultraviolet estimates are correct. But the possibility that the ultraviolet estimates have seriously underestimated the contribution of dust-shrouded star-formation can also not be excluded.
We investigate the relation between star formation rates ($\dot{M}_{s}$) and AGN properties in optically selected type 1 quasars at $2<z<3$ using data from Herschel and the SDSS. We find that $\dot{\rm{M}}_s$ remains approximately constant with redshift, at $300\pm100~\rm{M}_{\odot}$yr$^{-1}$. Conversely, $\dot{\rm{M}}_s$ increases with AGN luminosity, up to a maximum of $\sim600~\rm{M}_{\odot}$yr$^{-1}$, and with CIV FWHM. In context with previous results, this is consistent with a relation between $\dot{\rm{M}}_s$ and black hole accretion rate ($\dot{\rm{M}}_{bh}$) existing in only parts of the $z-\dot{\rm{M}}_{s}-\dot{\rm{M}}_{bh}$ plane, dependent on the free gas fraction, the trigger for activity, and the processes that may quench star formation. The relations between $\dot{\rm{M}}_s$ and both AGN luminosity and CIV FWHM are consistent with star formation rates in quasars scaling with black hole mass, though we cannot rule out a separate relation with black hole accretion rate. Star formation rates are observed to decline with increasing CIV equivalent width. This decline can be partially explained via the Baldwin effect, but may have an additional contribution from one or more of three factors; $M_i$ is not a linear tracer of L$_{2500}$, the Baldwin effect changes form at high AGN luminosities, and high CIV EW values signpost a change in the relation between $\dot{\rm{M}}_s$ and $\dot{\rm{M}}_{bh}$. Finally, there is no strong relation between $\dot{\rm{M}}_s$ and Eddington ratio, or the asymmetry of the CIV line. The former suggests that star formation rates do not scale with how efficiently the black hole is accreting, while the latter is consistent with CIV asymmetries arising from orientation effects.
The Far-InfraRed Spectroscopic Explorer (FIRSPEX) is a candidate mission in response to a bi-lateral Small-mission call issued by the European Space Agency (ESA) and the Chinese Academy of Sciences (CAS). FIRSPEX is a small satellite (~1m telescope) operating from Low Earth Orbit (LEO). It consists of a number of heterodyne detection bands targeting key molecular and atomic transitions in the terahertz (THz) and Supra-Terahertz (>1 THz) frequency range. The FIRSPEX bands are: [CII] 158 microns (1.9 THz), [NII] 205 microns (1.46 THz), [CI] 370 microns (0.89 THz), CO(6-5) 433 microns (0.69 THz). The primary goal of FIRSPEX is to perform an unbiased all sky spectroscopic survey in four far-infrared lines delivering the first 3D-maps (high spectral resolution) of the Galaxy. The spectroscopic surveys will build on the heritage of Herschel and complement the broad-band all-sky surveys carried out by the IRAS and AKARI observatories. In addition FIRSPEX will enable targeted observations of nearby and distant galaxies allowing for an in-depth study of the ISM components.
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.
In this work we explore the impact of the presence of an active galactic nucleus (AGN) on the mid- and far-infrared (IR) properties of galaxies as well as the effects of simultaneous AGN and starburst activity in these same galaxies. To do this we apply a multi-component, multi-band spectral synthesis technique to a sample of 250 micron selected galaxies of the Herschel Multi-tiered Extragalactic Survey, with IRS spectra available for all galaxies. Our results confirm that the inclusion of the IRS spectra plays a crucial role in the spectral analysis of galaxies with an AGN component improving the selection of the best-fit hot dust model (torus). We find a correlation between the obscured star formation rate (SFR) derived from the IR luminosity of the starburst component, SFR_IR and SFR_PAH, derived from the luminosity of the PAH features, L_PAH, with SFR_FIR taking higher values than SFR_PAH. The correlation is different for AGN- and starburst-dominated objects. The ratio of L_PAH to that of the starburst component, L_PAH/L_SB, is almost constant for AGN-dominated objects but decreases with increasing L_SB for starburst-dominated objects. SFR_FIR increases with the accretion luminosity, L_acc, with the increase less prominent for the very brightest, unobscured AGN-dominated sources. We find no correlation between the masses of the hot and cold dust components. We interpret this as a non-constant fraction of gas driven by the gravitational effects to the AGN while the starburst is ongoing. We also find no evidence of the AGN affecting the temperature of the cold dust component, though this conclusion is mostly based on objects with a non-dominant AGN component. We conclude that our findings do not provide evidence that the presence of AGN affects the star formation process in the host galaxy, but rather that the two phenomena occur simultaneously over a wide range of luminosities.
We perform a stacking analysis of H-ATLAS data in order to obtain isothermal dust temperatures and rest-frame luminosities at 250um (L250), for 1599 radio sources over the H-ATLAS P1 GAMA area. The radio sample is generated using a combination of NVSS data and K-band UKIDSS-LAS data, over 0.01 1.5 L_{K}^{*}) may have systematically lower FIR luminosities (~25%) than their colour-matched non radio-detected counterparts. Compact radio sources (<30kpc) are associated with higher L250s and dust temperatures than their more extended (>30kpc) counterparts. The higher dust temperature suggests that this may be attributed to enhanced SFRs, but whether this is directly or indirectly due to radio activity (e.g. jet induced or merger-driven SF) is as yet unknown.
Local luminous infrared (IR) galaxies (LIRGs) have both high star formation rates (SFR) and a high AGN (Seyfert and AGN/starburst composite) incidence. Therefore, they are ideal candidates to explore the co-evolution of black hole (BH) growth and star formation (SF) activity, not necessarily associated with major mergers. Here, we use Spitzer/IRS spectroscopy of a complete volume-limited sample of local LIRGs (distances of <78Mpc). We estimate typical BH masses of 3x10^7 M_sun using [NeIII]15.56micron and optical [OIII]5007A gas velocity dispersions and literature stellar velocity dispersions. We find that in a large fraction of local LIRGs the current SFR is taking place not only in the inner nuclear ~1.5kpc region, as estimated from the nuclear 11.3micron PAH luminosities, but also in the host galaxy. We next use the ratios between the SFRs and BH accretion rates (BHAR) to study whether the SF activity and BH growth are contemporaneous in local LIRGs. On average, local LIRGs have SFR to BHAR ratios higher than those of optically selected Seyferts of similar AGN luminosities. However, the majority of the IR-bright galaxies in the RSA Seyfert sample behave like local LIRGs. Moreover, the AGN incidence tends to be higher in local LIRGs with the lowest SFRs. All this suggests that in local LIRGs there is a distinct IR-bright star forming phase taking place prior to the bulk of the current BH growth (i.e., AGN phase). The latter is reflected first as a composite and then as a Seyfert, and later as a non-LIRG optically identified Seyfert nucleus with moderate SF in its host galaxy.
We report Herschel SPIRE (250, 350, and 500 micron) detections of 32 quasars with redshifts 0.5 < z < 3.6 from the Herschel Multi-tiered Extragalactic Survey. These sources are from a MIPS 24 micron flux-limited sample of 326 quasars in the Lockman Hole Field. The extensive multi-wavelength data available in the field permit construction of the rest-frame Spectral Energy Distributions (SEDs)from ultraviolet to the mid-infrared for all sources, and to the far-infrared (FIR) for the 32 objects. Most quasars with Herschel FIR detections show dust temperatures in the range of 25K to 60K, with a mean of 34K. The FIR luminosities range from 10^{11.3} to 10^{13.5} Lsun, qualifying most of their hosts as ultra- or hyper-luminous infrared galaxies. These FIR-detected quasars may represent a dust-rich population, but with lower redshifts and fainter luminosities than quasars observed at ~ 1 mm. However, their FIR properties cannot be predicted from shorter wavelengths (0.3--20 micron, rest-frame), and the bolometric luminosities derived using the 5100 A index may be underestimated for these FIR-detected quasars. Regardless of redshift, we observed a decline in the relative strength of FIR luminosities for quasars with higher near-infrared luminosities.
We quantify the active galactic nucleus (AGN) contribution to the mid-infrared (mid-IR) and the total infrared (IR, 8-1000micron) emission in a complete volume-limited sample of 53 local luminous infrared galaxies (LIRGs). We decompose the Spitzer Infrared Spectrograph (IRS) low-resolution 5-38micron spectra of the LIRGs into AGN and starburst components using clumpy torus models and star-forming galaxy templates, respectively. We find that 50% (25/50) of local LIRGs have an AGN component detected with this method. There is good agreement between these AGN detections through mid-IR spectral decomposition and other AGN indicators, such as the optical spectral class, mid-IR spectral features and X-ray properties. Taking all the AGN indicators together, the AGN detection rate in the individual nuclei of LIRGs is ~62%. The derived AGN bolometric luminosities are in the range L_bol(AGN)=0.4 -50x10^{43} erg/s. The AGN bolometric contribution to the IR luminosities of the galaxies is generally small, with 70% of LIRGs having L_bol(AGN)/L_IR<0.05. Only ~8% of local LIRGs have a significant AGN bolometric contribution L_bol(AGN)/L_IR > 0.25. From the comparison of our results with literature results of ultraluminous infrared galaxies, we confirm that in the local universe the AGN bolometric contribution to the IR luminosity increases with the IR luminosity of the galaxy/system. If we add up the AGN bolometric luminosities we find that AGNs only account for 5%^{+8%}_{-3%} of the total IR luminosity produced by local LIRGs (with and without AGN detections). This proves that the bulk of the IR luminosity of local LIRGs is due to star formation activity. Taking the newly determined IR luminosity density of LIRGs in the local universe, we then estimate an AGN IR luminosity density of Omega_IR(AGN) = 3x10^5 L_sun Mpc^{-3}$ in LIRGs.
We present a multi-wavelength, UV-to-radio analysis for a sample of massive (M$_{\ast}$ $\sim$ 10$^{10}$ M$_\odot$) IRAC- and MIPS 24$μ$m-detected Lyman Break Galaxies (LBGs) with spectroscopic redshifts z$\sim$3 in the GOODS-North field (L$_{\rm UV}$$>1.8\times$L$^{\ast}_{z=3}$). For LBGs without individual 24$μ$m detections, we employ stacking techniques at 24$μ$m, 1.1mm and 1.4GHz, to construct the average UV-to-radio spectral energy distribution and find it to be consistent with that of a Luminous Infrared Galaxy (LIRG) with L$\rm_{IR}$=4.5$^{+1.1}_{-2.3}$$\times 10^{11}$ L$_{\odot}$ and a specific star formation rate (SSFR) of 4.3 Gyr$^{-1}$ that corresponds to a mass doubling time $\sim$230 Myrs. On the other hand, when considering the 24$μ$m-detected LBGs we find among them galaxies with L$\rm_{IR}> 10^{12}$ L$_{\odot}$, indicating that the space density of $z\sim$3 UV-selected Ultra-luminous Infrared Galaxies (ULIRGs) is $\sim$(1.5$\pm$0.5)$\times 10^{-5}$ Mpc$^{-3}$. We compare measurements of star formation rates (SFRs) from data at different wavelengths and find that there is tight correlation (Kendall's $τ>$ 99.7%) and excellent agreement between the values derived from dust-corrected UV, mid-IR, mm and radio data for the whole range of L$\rm_{IR}$ up to L$\rm_{IR}$ $\sim$ 10$^{13}$ L$_{\odot}$. This range is greater than that for which the correlation is known to hold at z$\sim$2, possibly due to the lack of significant contribution from PAHs to the 24$μ$m flux at $z\sim$3. The fact that this agreement is observed for galaxies with L$\rm_{IR}$ $>$ 10$^{12}$ L$_{\odot}$ suggests that star-formation in UV-selected ULIRGs, as well as the bulk of star-formation activity at this redshift, is not embedded in optically thick regions as seen in local ULIRGs and submillimeter-selected galaxies at $z=2$.
Using a combination of deep MID-IR observations obtained by IRAC, MIPS and IRS on board Spitzer we investigate the MID-IR properties of Lyman Break Galaxies (LBGs) at z~3, establish a better understanding of their nature and attempt a complete characterisation of the population. With deep mid-infrared and optical observations of ~1000 LBGs covered by IRAC/MIPS and from the ground respectively, we extend the spectral energy distributions (SEDs) of the LBGs to mid-infrared. Spitzer data reveal for the first time that the mid-infrared properties of the population are inhomogeneous ranging from those with marginal IRAC detections to those with bright rest-frame near-infrared colors and those detected at 24mu MIPS band revealing the newly discovered population of the Infrared Luminous Lyman Break Galaxies (ILLBGs). To investigate this diversity, we examine the photometric properties of the population and we use stellar population synthesis models to probe the stellar content of these galaxies. We find that a fraction of LBGs have very red colors and large estimated stellar masses M* > 5x10^10Mo. We discuss the link between these LBGs and submm-luminous galaxies and we report the detection of rest frame 6.2 and 7.7mu emission features arising from Polycyclic Aromatic Hydrocarbons (PAH) in the Spitzer/IRS spectrum of an infrared-luminous Lyman break galaxy at z=3.01.
We present low resolution multi-object spectroscopy of an I-band magnitude limited (I_{AB} ~ 23--23.5) sample of galaxies located in an area centered on the Hubble Deep Field-South (HDFS). The observations were obtained using the Focal Reducer low dispersion Spectrograph (FORS) on the ESO Very Large Telescope. Thirty-two primary spectroscopic targets in the HST-WFPC2 HDFS were supplemented with galaxies detected in the Infrared Space Observatory's survey of the HDFS and the ESO Imaging Deep Survey to comprise a sample of 100 galaxies for spectroscopic observations. Based on detections of several emission lines, such as [OII]3727, H_beta and [OIII]5007, or other spectroscopic features, we have measured accurate redshifts for 50 objects in the central HDFS and flanking fields. The redshift range of the current sample of galaxies is 0.6--1.2, with a median redshift of 1.13 (at I ~ 23.5 not corrected for completeness). The sample is dominated by starburst galaxies with only a small fraction of ellipticals (~10%). For the emission line objects, the extinction corrected [OII]3727 line strengths yield estimates of star formation rates in the range 0.5--30 M_solar/yr. We have used the present data to derive the [OII]3727 luminosity function up to redshift of 1.2. When combined with [OII]3727 luminosity densities for the local and high redshift Universe, our results confirm the steep rise in the star formation rate (SFR) to z ~ 1.3.
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.