Stellar indices and kinematics in Seyfert 1 nuclei

We present spectra of six type 1 and two type 2 Seyfert galaxies, a starburst galaxy and a compact narrow-line radio galaxy, taken in two spectral ranges centred around the near-infrared Ca  ii triplet (∼8600 Å), and the Mgb stellar feature at 5180 Å. We measured the equivalent widths (EWs) of these features and the Fe₅₂ and Fe₅₃ spectral indices.
We found that the strength of the infrared Ca  ii triplet (CaT) in type 1 Seyfert galaxies with prominent central point sources is larger than what would be expected from the observed strength of the blue indices. This could be explained by the presence of red supergiants in the nuclei of Seyfert 1 galaxies. On the other hand, the blue indices of these galaxies could also be diluted by the strong Fe  ii multiplets that can be seen in their spectra.
We have also measured the stellar‐ and gas-velocity dispersions of the galaxies in the sample. The stellar velocity dispersions were measured using both the Mgb and CaT stellar features. The velocity dispersion of the gas in the narrow-line region (NLR) was measured using the strong emission lines [O  iii ] λλ 5007, 4959 and [S  iii ] λ 9069. We compare the gas- and star-velocity dispersions and find that the magnitudes of both are correlated in Seyfert galaxies.
Most of the Seyfert 1 galaxies that we observe have stellar‐velocity dispersions somewhat greater than that of the gas in the NLR.     

The host galaxies of active galactic nuclei

We examine the properties of the host galaxies of 22 623 narrow-line active galactic nuclei (AGN) with  0.02 < z < 0.3  selected from a complete sample of 122 808 galaxies from the Sloan Digital Sky Survey. We focus on the luminosity of the [O  iii ]λ5007 emission line as a tracer of the strength of activity in the nucleus. We study how AGN host properties compare with those of normal galaxies and how they depend on L [O  iii ]. We find that AGN of all luminosities reside almost exclusively in massive galaxies and have distributions of sizes, stellar surface mass densities and concentrations that are similar to those of ordinary early-type galaxies in our sample. The host galaxies of low-luminosity AGN have stellar populations similar to normal early types. The hosts of high-luminosity AGN have much younger mean stellar ages. The young stars are not preferentially located near the nucleus of the galaxy, but are spread out over scales of at least several kiloparsecs. A significant fraction of high-luminosity AGN have strong Hδ absorption-line equivalent widths, indicating that they experienced a burst of star formation in the recent past. We have also examined the stellar populations of the host galaxies of a sample of broad-line AGN. We conclude that there is no significant difference in stellar content between type 2 Seyfert hosts and quasars (QSOs) with the same [O  iii ] luminosity and redshift. This establishes that a young stellar population is a general property of AGN with high [O  iii ] luminosities.     

Deep spectroscopy of distant 3CR radio galaxies: the data

Deep long-slit spectroscopic data are presented for a sample of 14 3CR radio galaxies at redshift z ∼1, previously studied in detail using the Hubble Space Telescope , the Very Large Array, and the UK Infrared Telescope (UKIRT). Analysis of the [O  ii ] 3727 emission-line structures at ∼5 Å spectral resolution is carried out to derive the kinematic properties of the emission-line gas. In line with previous lower resolution studies, a wide variety of kinematics are seen, from gas consistent with a mean rotational motion through to complex structures with velocity dispersions exceeding 1000 km s ⁻¹. The data confirm the presence of a high-velocity gas component in 3C 265 and detached emission-line systems in 3C 356 and 3C 441, and show for the first time that the emission-line gas in the central regions of 3C 324 is composed of two kinematically distinct components. Emission-line fluxes and the colour of the continuum emission are determined down to unprecedentedly low observed wavelengths, λ <3500 Å, sufficiently short that any contribution of an evolved stellar population is negligible. An accompanying paper investigates the variation in the emission-line ratios and velocity structures within the sample, and draws conclusions as to the origin of the ionization and kinematics of these galaxies.     

New insights into the stellar content and physical conditions of star-forming galaxies at z= 2–3 from spectral modelling

We have used extensive libraries of model and empirical galaxy spectra [assembled, respectively, from the population synthesis code of Bruzual and Charlot and the fourth data release of the Sloan Digital Sky Survey (SDSS)] to interpret some puzzling features seen in the spectra of high-redshift star-forming galaxies. We show that a stellar He  ii  λ1640 emission line, produced in the expanding atmospheres of Of and Wolf–Rayet stars, should be detectable with an equivalent width of 0.5–1.5 Å in the integrated spectra of star-forming galaxies, provided the metallicity is greater than about half solar. Our models reproduce the strength of the He  ii  λ1640 line measured in the spectra of Lyman-break galaxies for established values of their metallicities. With better empirical calibrations in local galaxies, this spectral feature has the potential of becoming a useful diagnostic of massive star winds at high, as well as low redshifts.
We also uncover a relationship in SDSS galaxies between their location in the [O  iii ]/Hβ versus [N  ii ]/Hα diagnostic diagram (the BPT diagram) and their excess specific star formation rate relative to galaxies of similar mass. We infer that an elevated ionization parameter U is at the root of this effect, and propose that this is also the cause of the offset of high-redshift star-forming galaxies in the BPT diagram compared to local ones. We further speculate that higher electron densities and escape fractions of hydrogen ionizing photons may be the factors responsible for the systematically higher values of U in the H  ii regions of high-redshift galaxies. The impact of such differences on abundance determinations from strong nebular lines are considered and found to be relatively minor.     

Emission-line properties of Seyfert 2 nuclei

This is the third paper of a series devoted to the study of the global properties of Joguet's sample of 79 nearby galaxies observable from the southern hemisphere, of which 65 are Seyfert 2 galaxies. We use the population synthesis models of Paper II to derive 'pure' emission-line spectra for the Seyfert 2 galaxies in the sample, and thus explore the statistical properties of the nuclear nebular components and their relation to the stellar populations. We find that the emission-line clouds suffer substantially more extinction than the starlight, and we confirm the correlations between stellar and nebular velocity dispersions and between emission-line luminosity and velocity dispersions, although with substantial scatter. Nuclear luminosities correlate with stellar velocity dispersions, but Seyferts with conspicuous star-forming activity deviate systematically towards higher luminosities. Removing the contribution of young stars to the optical continuum produces a tighter and steeper relation,   L ∝σ⁴_★  , consistent with the Faber–Jackson law.
Emission-line ratios indicative of the gas excitation such as [O  iii ]/Hβ and [O  iii ]/[O  ii ] are statistically smaller for Seyferts with significant star formation, implying that ionization by massive stars is responsible for a substantial and sometimes even a dominant fraction of the Hβ and [O  ii ] fluxes. We use our models to constrain the maximum fraction of the ionizing power that can be generated by a hidden active galactic nucleus (AGN). We correlate this fraction with classical indicators of AGN photoionization (i.e. X-ray luminosity and nebular excitation), but find no significant correlations. Thus, while there is a strong contribution of starbursts to the excitation of the nuclear nebular emission in low-luminosity Seyferts, the contribution of the hidden AGN remains elusive even in hard X-rays.     

Stellar velocity dispersion in narrow-line Seyfert 1 galaxies

Several authors have recently explored, for narrow-line Seyfert 1 galaxies (NLS1s), the relationship between black hole mass ( M _BH) and stellar velocity dispersion (σ_*). Their results are more or less in agreement and seem to indicate that NLS1s fill the region below the fit obtained by Tremaine et al., showing a range of σ_* similar to that of Seyfert 1 galaxies, and a lower M _BH. Until now, the [O  iii ] width has been used in place of the stellar velocity dispersion, but some indications have begun to arise against the effectiveness of the gaseous kinematics in representing the bulge potential, at least in NLS1s. Bian & Zhao have stressed the urgency of producing true σ_* measurements. Here, we present new stellar velocity dispersions obtained through direct measurements of the Ca  ii absorption triplet (∼8550 Å) in the nuclei of eight NLS1 galaxies. The resulting σ_* values and a comparison with σ_[O III] confirm our suspicion that [O  iii ] typically overestimates the stellar velocity dispersion. We demonstrate that NLS1s follow the   M _BH–σ_*  relation as Seyfert 1, quasars and non-active galaxies.     

Star formation rates and chemical abundances of emission-line galaxies in intermediate-redshift clusters

We examine the evolutionary status of luminous, star-forming galaxies in intermediate-redshift clusters by considering their star formation rates (SFRs) and the chemical and ionization properties of their interstellar emitting gas. Our sample consists of 17 massive, star-forming, mostly disc galaxies with   M_B ≲−20  , in clusters with redshifts in the range  0.31 ≲ z ≲ 0.59  , with a median of  〈 z 〉= 0.42  . We compare these galaxies with the identically selected and analysed intermediate-redshift field sample of Mouhcine et al., and with local galaxies from the Nearby Field Galaxy Survey of Jansen et al.
From our optical spectra, we measure the equivalent widths of  [O  ii ]λ3727, Hβ  and [O  iii ]λ5007 emission lines to determine diagnostic line ratios, oxygen abundances and extinction-corrected SFRs. The star-forming galaxies in intermediate-redshift clusters display emission-line equivalent widths which are, on average, significantly smaller than measured for field galaxies at comparable redshifts. However, a contrasting fraction of our cluster galaxies have equivalent widths similar to the highest observed in the field. This tentatively suggests a bimodality in the SFRs per unit luminosity for galaxies in distant clusters. We find no evidence for further bimodalities, or differences between our cluster and field samples, when examining additional diagnostics and the oxygen abundances of our galaxies. This maybe because no such differences exist, perhaps because the cluster galaxies which still display signs of star formation have recently arrived from the field. In order to examine this topic with more certainty, and to further investigate the way in which any disparity varies as a function of cluster properties, larger spectroscopic samples are needed.     

The CaT strength in Seyfert nuclei revisited: analysing young stars and non-stellar light contributions to the spectra

In a former paper, we have presented spectra of 64 active, nine normal and five starburst galaxies in the region around the near-infrared calcium triplet (CaT) absorption lines and the [S  iii ]λ9069 line. In the present paper, we analyse the CaT strength ( W _CaT) and kinematical products derived in that study, namely stellar  (σ_★)  and ionized gas (σ_gas) velocity dispersions. Our main results may be summarized as follows. (1) Type 2 Seyfert galaxies show no sign of dilution in W _CaT with respect to the values spanned by normal galaxies, even when optical absorption lines such as the Ca  ii K band at 3933 Å are much weaker than in old, bulge-like stellar populations. (2) The location of type 2 Seyfert galaxies in the   W _CaT– W _CaK  plane is consistent with evolutionary synthesis models. The implication is that the source responsible for the dilution of optical lines in these active galactic nuclei (AGN) is a young stellar population, rather than an AGN featureless continuum, confirming the conclusion of the pioneer study of Terlevich, Díaz & Terlevich. (3) In type 1 Seyfert galaxies, both   W _{[S  iii ]}  and W _CaT tend to be diluted due to the presence of a non-stellar component, in agreement with the unification paradigm. (4) A comparison of  σ_★  with σ_gas (obtained from the core of the [S  iii ] emitting line) confirms the existence of a correlation between the typical velocities of stars and clouds of the narrow line region. The strength and scatter around this correlation are similar to those previously obtained from the [O  iii ]λ5007 linewidth.     

Gas properties of H ii and starburst galaxies: relation with the stellar population

We study the gas emission of galaxies with active star formation, consisting mostly of H  ii and starburst galaxies, as well as some Seyfert 2 galaxies, and determine chemical and physical parameters. The data consist of 19 high signal-to-noise ratio optical templates, a result of grouping 185 emission-line galaxy spectra. Underlying stellar population models (from Raimann et al.) were subtracted from the templates in order to isolate the pure emission component.
We analyse the distribution of these improved signal-to-noise ratio emission spectra in diagnostic diagrams and find that the H  ii templates show a smaller spread in log([O  iii ]/H β ) values than the individual galaxies, apparently as a result of the population subtraction and a better signal-to-noise ratio. We thus suggest the template sequence as a fiducial observational locus for H  ii galaxies which can be used as reference for models. The sequence of line ratios presented by the H  ii galaxies in the diagram log([O  iii ] λ 5007/H β ) versus log([N  ii ] λ 6584/H α ) is primarily owing to the gas metallicity, of which the log([N  ii ]/H α ) ratio is a direct estimator. We also study the properties of the starburst galaxies and those intermediate between H  ii and starburst galaxies, which are more metal rich and sit on more massive galaxies.
We discuss the present results in the frame of a recently proposed equivalent-width diagnostic diagram for emission-line galaxies (by Rola et al.) and conclude that the observed ranges in W ([O  ii ])/ W (H β ) and W (H β ) are mostly owing to the non-ionizing stellar population contribution. We propose that W (H β ) be used as an estimator of this contribution to the continuum, and briefly discuss implications to the cosmological use of H  ii galaxies.     

The SAURON project – VII. Integral-field absorption and emission-line kinematics of 24 spiral galaxy bulges

We present observations of the stellar and gas kinematics for a representative sample of 24 Sa galaxies obtained with our custom-built integral-field spectrograph SAURON operating on the William Herschel Telescope. The data have been homogeneously reduced and analysed by means of a dedicated pipeline. All resulting data cubes were spatially binned to a minimum mean signal-to-noise ratio of 60 per spatial and spectral resolution element. Our maps typically cover the bulge-dominated region. We find a significant fraction of kinematically decoupled components (12/24), many of them displaying central velocity dispersion minima. They are mostly aligned and co-rotating with the main body of the galaxies, and are usually associated with dust discs and rings detected in unsharp-masked images. Almost all the galaxies in the sample (22/24) contain significant amounts of ionized gas which, in general, is accompanied by the presence of dust. The kinematics of the ionized gas are consistent with circular rotation in a disc co-rotating with respect to the stars. The distribution of mean misalignments between the stellar and gaseous angular momenta in the sample suggests that the gas has an internal origin. The [O  iii ]/Hβ ratio is usually very low, indicative of current star formation, and shows various morphologies (ring-like structures, alignments with dust lanes or amorphous shapes). The star formation rates (SFRs) in the sample are comparable with that of normal disc galaxies. Low gas velocity dispersion values appear to be linked to regions of intense star formation activity. We interpret this result as stars being formed from dynamically cold gas in those regions. In the case of NGC 5953, the data suggest that we are witnessing the formation of a kinematically decoupled component from cold gas being acquired during the ongoing interaction with NGC 5954.     

Are there any Type 2 QSOs? The case of AXJ0341.4–4453

The X-ray source AXJ0341.4–4453 was described by Boyle et al. as a Type 2 active galactic nucleus (AGN) at z =0.672 based on the absence of broad emission lines in the observed wavelength range 4000–7000 Å. We obtained a new spectrum of AXJ0341.4–4453 extending to 9600 Å which reveals broad Balmer lines and other characteristics of Seyfert 1 galaxies. The FWHM of broad H β is at least 1600 km s⁻¹, while [O  iii ] λ 5007 has FWHM=730 km s⁻¹. The flux ratio [O  iii ] λ 5007/H β =1. Thus, AXJ0341.4–4453 is by definition a narrow-line Seyfert 1 galaxy, or perhaps a moderately reddened Seyfert 1 galaxy, but it is not a Type 2 QSO. Although examples of the latter have long been sought, particularly in connection with the problem of the X-ray background, there is still virtually no evidence for the existence of any Type 2 QSO among X-ray selected samples.     

The Hα luminosity function and star formation rate up to z ∼ 1

We describe ISAAC/ESO-VLT observations of the Hαλ6563 Balmer line of 33 field galaxies from the Canada–France Redshift Survey (CFRS) with redshifts selected between 0.5 and 1.1. We detect Hα in emission in 30 galaxies and compare the properties of this sample with the low-redshift sample of CFRS galaxies at   z ∼ 0.2  . We find that the Hα luminosity,   L (Hα)  , is tightly correlated to   M ( B _AB)  in the same way for both the low- and high-redshift samples.   L (Hα)  is also correlated to L ([O  ii ]λ3727), and again the relation appears to be similar at low and high redshifts. The ratio L (lsqb;O  ii ])/   L (Hα)  decreases for brighter galaxies by as much as a factor of 2 on average. Derived from the Hα luminosity function, the comoving Hα luminosity density increases by a factor 12 from  〈 z 〉= 0.2  to  〈 z 〉= 1.3  . Our results confirm a strong rise of the star formation rate (SFR) at   z < 1.3  , proportional to  (1 + z )^4.1±0.3  (with   H ₀= 50 km s⁻¹ Mpc⁻¹, q ₀= 0.5  ). We find an average  SFR(2800 Å)/SFR (Hα)  ratio of 3.2 using the Kennicutt SFR transformations. This corresponds to the dust correction that is required to make the near-ultraviolet data consistent with the reddening-corrected Hα data within the self-contained, I -selected CFRS sample.     

Global velocity field and bubbles in the blue compact dwarf galaxy Mrk 86

We have studied the velocity field of the blue compact dwarf galaxy Mrk 86 (NGC 2537) using data provided by 14 long-slit optical spectra obtained in 10 different orientations and positions. This kinematical information is complemented with narrow-band ([O  iii ]5007 Å and H α ) and broad-band ( B , V , Gunn r and K ) imaging. The analysis of the galaxy global velocity field suggests that the ionized gas could be distributed in a rotating inclined disc, with projected central angular velocity of Ω=34 km s⁻¹ kpc⁻¹. The comparison between the stellar, H  i and modelled dark matter density profile indicates that the total mass within its optical radius is dominated by the stellar component. Peculiarities observed in its velocity field can be explained by irregularities in the ionized gas distribution or local motions induced by star formation.
Kinematical evidences for two expanding bubbles, Mrk 86–B and Mrk 86–C, are given. They show expanding velocities of 34 and 17 km s⁻¹, H α luminosities of 3×10³⁸ and 1.7×10³⁹ erg s⁻¹, and physical radii of 374 and 120 pc, respectively. The change in the [S  ii ]/H α , [N  ii ]/H α , [O  ii ]/[O  iii ] and [O  iii ]/H β line ratios with the distance to the bubble precursor suggests a diminution in the ionization parameter and, in the case of Mrk 86–B, an enhancement of the shock-excited gas emission. The optical–near-infrared colours of the bubble precursors are characteristic of low‐metallicity star‐forming regions (∼0.2 Z_⊙) with burst strengths of about 1 per cent in mass.     

Hα photometry of Abell 2390

We present the results of a search for strong H α emission line galaxies (rest frame equivalent widths greater than 50 Å) in the z ≈0.23 cluster Abell 2390. The survey contains 1189 galaxies over 270 arcmin², and is 50 per cent complete at M _r ≈−17.5+5 log  h . The fraction of galaxies in which H α is detected at the 2 σ level rises from 0.0 in the central regions (excluding the cD galaxy) to 12.5±8 per cent at R ₂₀₀. For 165 of the galaxies in our catalogue, we compare the H α equivalent widths with their [O  ii ] λ 3727 equivalent widths, from the Canadian Network for Observational Cosmology (CNOC1) spectra. The fraction of strong H α emission line galaxies is consistent with the fraction of strong [O  ii ] emission galaxies in the CNOC1 sample: only 2±1 per cent have no detectable [O  ii ] emission and yet significant (>2 σ ) H α equivalent widths. Dust obscuration, non-thermal ionization, and aperture effects are all likely to contribute to this non-correspondence of emission lines. We identify six spectroscopically 'secure' k+a galaxies [ W ₀(O  ii )<5 Å and W ₀(H δ )≳5 Å]; at least two of these show strong signs in H α of star formation in regions that are covered by the slit from which the spectra were obtained. Thus, some fraction of galaxies classified as k+a based on spectra shortward of 6000 Å are likely to be undergoing significant star formation. These results are consistent with a 'strangulation' model for cluster galaxy evolution, in which star formation in cluster galaxies is gradually decreased, and is neither enhanced nor abruptly terminated by the cluster environment.     

Emission-line outflows in PKS1549−79: the effects of the early stages of radio-source evolution?

We present new spectroscopic observations of the southern radio galaxy         . Despite the flat-spectrum character of the radio emission from this source, our optical spectra show no sign of the broad permitted lines and non-stellar continuum characteristic of quasar nuclei and broad-line radio galaxies. However, the high-ionization forbidden lines, including [O  iii ] λλ 5007, 4959, are unusually broad for a narrow-line radio galaxy     , and are blueshifted by 600 km s⁻¹ relative to the low-ionization lines such as [O  ii ] λλ 3726,3729. The [O  ii ] lines are also considerably narrower     than the [O  iii ] lines, and have a redshift consistent with that of the recently detected H  i 21-cm absorption-line system. Whereas the kinematics of the [O  iii ] emission lines are consistent with outflow in an inner narrow-line region, the properties of the [O  ii ] emission lines suggest that they are emitted by a more extended and quiescent gaseous component. We argue that, given the radio properties of the source, our line of sight is likely to be lying close to the direction of bulk outflow of the radio jets. In this case it is probable that the quasar nucleus is entirely obscured at optical wavelengths by the material responsible for the H  i absorption-line system. The unusually broad [O  iii ] emission lines suggest that the radio source is intrinsically compact. Overall, our data are consistent the idea that     is a radio source in an early stage of evolution.     

Specific angular momentum of disc merger remnants and the λR-parameter

We use two-dimensional kinematic maps of simulated binary disc mergers to investigate the  λ_R  -parameter, which is a luminosity-weighted measure of projected angular momentum per unit mass. This parameter was introduced to subdivide the SAURON sample of early-type galaxies in so-called fast  λ_R > 0.1  and slow rotators  λ_R < 0.1  . Tests on merger remnants reveal that  λ_R  is a robust indicator of the true angular momentum content in elliptical galaxies. We find the same range of  λ_R  values in our merger remnants as in the SAURON galaxies. The merger mass ratio is decisive in transforming fast rotators into slow rotators in a single binary merger, the latter being created mostly in an equal-mass merger. Slow rotators have a  λ_R  which does not vary with projection. The confusion rate with face-on fast rotators is very small. Mergers with a gas component form slow rotators with smaller ellipticities than collisionless merger remnants have, and are in much better agreement with the SAURON slow rotators. Remergers of merger remnants are slow rotators, but tend to have too high ellipticities. Fast rotators maintain the angular momentum content from the progenitor disc galaxy if merger mass ratio is high. Some SAURON galaxies have values of  λ _R   as high as our progenitor disc galaxies.     

Planetary nebula velocities in the disc and bulge of M31

We present radial velocities for a sample of 723 planetary nebulae in the disc and bulge of M31, measured using the WYFFOS fibre spectrograph on the William Herschel Telescope. Velocities are determined using the [O  iii ] λ5007 emission line. Rotation and velocity dispersion are measured to a radius of 50 arcmin (11.5 kpc), the first stellar rotation curve and velocity dispersion profile for M31 to such a radius. Our kinematics are consistent with rotational support at radii well beyond the bulge effective radius of 1.4 kpc, although our data beyond a radius of 5 kpc are limited. We present tentative evidence for kinematic substructure in the bulge of M31 to be studied fully in a later work. This paper is part of an ongoing project to constrain the total mass, mass distribution and velocity anisotropy of the disc, bulge and halo of M31.     

The UKIRT Infrared Deep Sky Survey ZY JHK photometric system: passbands and synthetic colours

We present a statistical study of a very large sample of H  ii galaxies taken from the literature. We focus on the differences in several properties between galaxies that show the auroral line [O  iii ]λ4363 and those that do not present this feature in their spectra. It turns out that objects without this auroral line are more luminous, are more metal-rich and present a lower ionization degree. The underlying population is found to be much more important for objects without the [O  iii ]λ4363 line, and the effective temperature of the ionizing star clusters of galaxies not showing the auroral line is probably lower. We also study the subsample of H  ii galaxies whose properties most closely resemble the properties of the intermediate-redshift population of luminous compact blue galaxies (LCBGs). The objects from this subsample are more similar to the objects not showing the [O  iii ]λ4363 line. It might therefore be expected that the intermediate- redshift population of LCBGs is powered by very massive, yet somewhat aged, star clusters. The oxygen abundance of LCBGs would be greater than the average oxygen abundance of local H  ii galaxies.     

Overpressured emission-line clouds in the haloes of powerful radio galaxies

We present accurate measurements of the physical conditions in five powerful radio galaxies, as derived from deep, long-slit spectroscopic observations. All five objects show prominent extended line emission, and have X-ray luminosities similar to those of isolated elliptical galaxies. The data are high enough quality that the electron density and temperature can be measured at several positions across the emission-line nebulae.
We subtract a model continuum comprising a combination of a 15-Gyr stellar template, a young stellar template and a power law, so as to be better able to measure faint diagnostic lines. Electron temperatures measured from the [O  iii ](4959+5007)/4363 line ratio are in the range  10 000< T _e<20 000 K  , whilst  [S  ii ](6716/6731)  densities fall between  100–500 cm^-3.  Using these values, we find pressures within the line-emitting clouds a factor of  10–100  times higher than expected for pressure balance with the hot X-ray haloes of the host galaxies.
Previous studies of sources that show significant evidence of jet–cloud interactions, both in terms of their kinematics and ionization, have concluded that the overpressure is a result of the warm, line-emitting gas being compressed by the radio cocoon; however, there is no evidence that the radio jet is influencing the emission-line regions in four of our five objects.
We suggest that it is plausible that the line-emitting clouds have not yet relaxed into pressure equilibrium from their initial photoionization by the central active galactic nucleus.     

On the origin and excitation of the extended nebula surrounding NGC 1275

We use line-of-sight velocity information on the filamentary emission-line nebula of NGC 1275 to infer a dynamical model of the nebula's flow through the surrounding intracluster gas. We detect outflowing gas and flow patterns that match simulations of buoyantly rising bubbles from which we deduce that some of the nebula filaments have been drawn out of NGC 1275. We find a radial gradient of the ratio [N  ii ]λ6584/Hα which may be due to a variation in metallicity, interactions with the surrounding intracluster medium or a hardening of the excitation mechanism. We find no preferred spatial correlation of stellar clusters within the filaments and there is a notable lack of [O  iii ]λ5007 emission, therefore it is unlikely that the filaments are ionized by stellar ultraviolet.