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Notes for object NGC 4051

40 note(s) found in NED.


1. 2009ApJ...705..962C
Re:NGC 4051
No high-velocity gas is detected in the Si III profile, nor in any other
absorption lines. We estimate an upper limit on high-velocity N_Si III_ by
assuming a width of 100 km s^-1^ for any possible feature.

2. 2007MNRAS.379.1249D
Re:NGC 4051
NGC 4051 is an SAB galaxy classified as S1.2 by Ho et al. (1997). The stellar
bar extends up to ~50 arcsec along a PA ~135{degrees}. Radio observations show a
triple source at a PA ~73{degrees} (Christopoulou et al. 1997), and the [O III]
emission-line distribution in the inner 3 arcsec is aligned with this radio
component. The narrow-line profiles of NGC 4051 present strong blue wings. This
blueshifted component is also detected with SAURON in the H{beta} and [O III]
lines, and has therefore been fitted (see Section 2.4). Christopoulou et al.
(1997) found evidence for a conical outflow, at 1.5 arcsec from the nucleus.
Our SAURON stellar continuum map (Fig. 4d) shows regular isophotes elongated
along the PA of the large scale bar. The stellar velocity field presents a
regular and symmetric rotation pattern, the rotation axis being aligned with the
photometric major-axis (PA ~ 135{degree}). The stellar velocity dispersion
decreases in the inner 5 arcsec down to ~50 km s^-1^.
The emission-line intensity is slightly extended towards the north-east,
consistent with the ionized [O III] outflow cone observed by Christopoulou et
al. (1997). The orientation of the ionized gas kinematic major-axis varies with
radius; it is aligned with the stellar major-axis in the outer part of the
SAURON FOV, and then deviates by about 30{degree} from the LON of the galaxy.
The H{beta} emission-line velocity dispersion reaches its highest values in the
inner 5 arcsec, while a decrease of dispersion is observed in these central
regions for [O iii]. The [O III]/H{beta} line ratio peaks at about 3 arcsec
north-east from the nucleus, within the outflow region (Christopoulou et al.
1997).

3. 2007AJ....134.1061D
Re:NGC 4051
NGC 4051 shows a broad absorbing region that has no real contamination in the O
VI blue member. The O VI red member is visible, but an O I dayglow line lies
inside the trough, and the Ly{beta} has a similar problem, with an O I dayglow
line alongside the Ly{beta} dayglow line. Using STIS, Collinge et al. (2001)
found two absorbing systems, one at approximately -600 km s^-1^ and one at
approximately -2400 km s^-1^. Each of these broad components break into up to
eight smaller components in STIS spectra in the C IV and N V lines. In the FUSE
data we see only the lower velocity component. There is no evidence in the FUSE
spectrum for a higher velocity component.

4. 2007A&A...461.1209D
Re:NGC 4051
NGC 4051: This narrow-line Seyfert 1 was observed twice by BeppoSAX.
During the first observation (observation a), the source was observed in
an unusual low state during which the X-ray spectrum was dominated by a
reflection component (Guainazzi et al. 1998). This is also confirmed by
the present analysis of the data. The second BeppoSAX observation of the
source, taken one-and-an-half-months later, was never published. The
source was an order of magnitude brighter than during observation a, and
the X-ray spectrum is simply modeled by a power law. No low-energy
cut-off due to cold or mildly ionized absorption is measured.
Nonetheless, a prominent absorption edge is detected at E~7.1 keV (i.e.,
well in agrement with being produced by cold matter). The addition of a
reflection component and/or a partial covering is not required, on
statistical basis, by the data. This is also true for the FeK{alpha}
emission line.

5. 2006MNRAS.365.1067C
Re:NGC 4051
5.4 NGC 4051
The observation of NGC 4051 we analyse is of very high quality, and shows some
features not observable in any of the other sources. It is clear from Fig. 7
that the disc reflection model follows the shape of the continuum very well,
but there are several small features which contribute to the fairly high
{chi}^2^_{nu}_ of 1.240 for 1040 d.o.f. Some of these features may be
calibration problems, such as around the XMM Newton instrumental Au M edge
at 2.3 keV, and some may be due to small amounts of absorption or emission.
However, it is also possible that some of the approximations made in the disc
reflection model are invalid when analysing observations of this detail (see
Section 6). A more detailed analysis of NGC 4051 and its variability using the
disc reflection model is in Ponti et al. (in preparation).

6. 2006A&A...457...61R
Re:NGC 4051
NGC 4051. One of the most well-studied AGN of our sample, NGC 4051 is
classified as a NLS1 galaxy. Our NIR spectrum reveals a large variety
of spectroscopic features, from low ionization forbidden lines such as,
[C I] and [N I], to high-ionization lines of [S IX] and [Si X]. The
last two are particularly strong, compared to the other emission lines
observed. The NLS1 nature of NGC 4051 is revealed well by the width of
permitted lines. The FWHM of O I 11 287 Angstrom, an exclusive BLR
feature free of contamination from the NLR, is only 940 km s^-1^.
Moreover, the broad component of H I and He I is 1200 km s^-1^. We also
report the detection of several permitted Fe II lines, including the
ones near 9200 Angstrom, attributed to Ly{alpha} fluorescence processes
(Sigut & Pradhan 1998,2003). The continuum emission is clearly
composite and steep, decreasing in flux towards longer wavelengths.
Underlying stellar population is observed, as can be seen from
absorption lines of CO, including the bandheads at 2.3 microns. Towards
the blue edge of the spectrum, a small excess of emission is seen.

7. 2005ApJS..160...76B
Re:NGC 4051
Significant discordance and low S/N. The large peak signal is due to the AGN.
Regular rotation, patchy {sigma}_*_ field and a steep curve of growth. There are
large values for both h_3_ and h_4_, the signature of a large asymmetry and
super-Gaussian wings in the LOSVD. See Figures 19 and 20d.

8. 2004ApJ...613..682P
Re:NGC 4051
NGC 4051. This object was also studied recently by Shemmer et
al. (2003), who obtain a black hole mass consistent with the results of
Peterson et al. (2000), who present the data we have used here.

9. 2003AJ....126..742H
Re:NGC 4051
The morphological classification as determined by us is indicated in
parentheses next to the galaxy name, with our "chaotic circumnuclear
dust" (C) category now not including those galaxies with obvious dust
lanes (DL). Where the classification has already been made by Martini
et al. (2003), we indicate this with "-mp."
.
3.20. NGC 4051
Figure 10 (top).
Spectra: Strong broad features with little extended emission.
Continuum is strong only in the NUC spectrum.

10. 2002ApJS..143...73E
Re:NGC 4051
NGC 4051.---SBb: Bright nuclear point source embedded in an elliptical
bulge. Bulge is threaded by a prominent bar aligned with the bulge
major axis. System has a complex, multiarm spiral pattern, with two
dominant arms that emerge from the ends of the bar. There are also two
fainter arms. One emerges from the west end of the bulge. The other
appears to form via the bifurcation of the southern main arm. The arms
are rich in substructure and star-forming knots.

11. 2002AJ....124..675C
Re:UGC 07030
CfA Seyfert 1 (Huchra & Burg 1992).

12. 2002A&A...389...68G
Re:NGC 4051
NGC 4051: the HII region distribution is somewhat irregular and the
first method gives results only in rough agreement with the values
from the second method. We finally adopt the kinematical values of
Listz & Dickey (1995), which are in general agreement with most of
the photometric values.

13. 2001ApJS..136...61S
Re:NGC 4051
5.20. NGC 4051
NGC 4051 has been referred to as the least luminous "classical"
Seyfert 1 (Ho et al. 1997b; Weedman 1976). HST archive [O III] emission
line imaging (Schmitt & Kinney 1996) reveals an unresolved nuclear source
with fainter extended (1.2") emission along a position angle of 100^deg^,
similar to the radio continuum structure observed by Ulvestad & Wilson
(1984a). Veilleux (1991), in his study of the structure and kinematics of
the narrow line regions in Seyfert galaxies, notes that the line profiles
of all of the observed forbidden lines show pronounced blue wings. There
are no corresponding red wings, which led him to propose a model including
outflow toward us plus dust obscuration to extinct the flow away from us.
Hot dust has also been invoked to explain the mid- and far-infrared
continuum emission (Rodriguez Espinosa et al. 1996; Contini & Viegas 1999);
the former authors differentiate between hot dust heated by the AGN and
somewhat cooler dust which is heated by star formation. Variability of
NGC 4051 occurs on a number of different timescales. Salvati et al. (1993)
report an outburst at 2.2 microns of more than a factor of 2 in 6 months in
1992, over which time the UV emission appears to be less variable. X-ray
variability with timescales as short as a few hundred seconds has been
observed by EXOSAT (Lawrence et al. 1985), while Done et al. (1990) report
on observations of strong X-ray variations within timescales of tens of
minutes. Finally, Singh (1999) present a high-resolution X-ray map for the
nuclear region (5"-10") of NGC 4051 and interpret it as due to central
(nuclear) activity plus an extended starburst component.

14. 2001ApJS..133...77H
Re:NGC 4051
NGC 4051 (S1.2). - The radio structure of the nuclear region is known
to be quite complex. At the highest available resolution, the central core
splits into a small-scale double separated by 0.4" roughly in the east-west
direction (Ulvestad & Wilson 1984b, 6 cm, {DELTA}{theta} = 0.4"; Kukula
et al. 1995, 3.6 cm, {DELTA}{theta} = 0.3"). On a somewhat coarser
resolution of ~1", however, particularly at 20 cm, the source is dominated
by emission extending toward the southwest (Ulvestad & Wilson 1984b;
Vila et al. 1990). We detected this extended component in our maps, both
at 6 and 20 cm, but we additionally see a fainter, oppositely directed
component to the northeast. The two-sidedness of the extended component is
best viewed in our tapered 6 cm map; it can also be seen in the
{DELTA}{theta} ~ 4" 6 cm WSRT map of Baum et al. (1993). The total linear
extent of the "jet" is 1.2 kpc, and it lies along P.A. = 41^deg^,
perpendicular to the host-galaxy major axis (P.A. = 135^deg^). We note, in
passing, that the nucleus appears to be quite variable at 6 cm. The
existing measurements made with {DELTA}{theta} ~ 1" show a spread of a
factor of 6 in the 6 cm flux density (van der Hulst et al. 1981, 3.5 mJy;
Ulvestad & Wilson 1984b, 6.0 mJy; Vila et al. 1990, 0.9 mJy; this paper,
3.2 mJy).

15. 2001ApJ...550..261W
Re:NGC 4051
3.3.6. NGC 4051
The 2-10 keV flux decreases by ~10% between the two ASCA pointings
approximately 1 yr apart (Fig. 8f). We do not detect any changes in the
iron line between the two observations, but the continuum varies by as much
as a factor of ~6 on timescales of a few hours, and the short-term
variability of the line has been investigated in detail by Wang et al.
(1999b). Using a model that consists of a single power law and narrow
Gaussian, these authors find that the line profile changes in ways that are
independent of the continuum. A very interesting result is that the EW of
the Fe K line in NGC 4051 increases as the source brightens (Wang et al.
1999b), as opposed to MCG -6-30-15, where the EW decreases as the source
brightens (see also Wang et al. 1999b).

16. 2001AJ....122..637H
Re:NGC 4051
NGC 4051. - Komossa & Fink (1997) used a warm absorber model to derive
an X-ray flux of 4.0 x 10^-11^ ergs cm^-2^ s^-1^. While this is higher
than the flux we measured, they also used a different PSPC observation, in
which the count rate of this highly variable object was greater than the
count rate for the observation we selected.

17. 2001A&A...372..730V
Re:NGC 4051
NGC 4051 (1200+44) is an NLS1 (Leighly 1999a). The H{beta} FWHM is 990
(De Robertis & Osterbrock 1984) or 1150 km s^-1^ (Leighly 1999b). The
coronal lines are strong (Grandi 1978; Veilleux 1988; Erkens et al. 1997).
Peterson et al. (2000) found that the Balmer lines could arise in a
disk-like configuration and the high-ionization lines in an outflowing
wind, of which we observe preferentially the near side. The structure and
the kinematics of the [O III] lines also suggest an outflow
(Christopoulou et al. 1997).
Our observations show the presence of two components in the
[O III] lines, a narrow one (200 km s^-1^ FWHM) and a broader one
(665 km s^-1^ FWHM) blueshifted by 175 km s^-1^ with respect to the first.
The X-ray source is variable by at least a factor 30 (Papadakis &
Lawrence 1995; Leighly 1999a; Uttley et al. 1999; Komossa &
Meerschweinchen 2000); long term variations in the average X-ray flux might
in principle be caused by absorption by a varying column of material along
the line of sight; but this is ruled out by the spectral data; it is the
2-10 keV luminosity which shows large amplitude long-term variations
(Uttley et al. 1999).

18. 2001A&A...368...16M
Re:NGC 4051
29. NGC 4051 is an Sbc spiral of medium inclination. It is a well
investigated Seyfert galaxy. The light contribution of the active nucleus
was not considered in the fit, a corresponding tiny residuum can be seen
in Fig. 5 (in on-line version).

19. 2000A&A...354..411K
Re:NGC 4051
4.3. NGC 4051
NGC 4051 has been classified as Seyfert 1.8 (e.g., Rosenblatt et al.
1992) or NLSy1 (e.g., Malkan 1986) and is at a redshift of z = 0.0023.
This galaxy has been observed with all major X-ray satellites
(e.g., Marshall et al. 1983, Lawrence et al. 1985, Matsuoka et al. 1990,
Mihara et al. 1994, McHardy et al. 1995, Guainazzi et al. 1996, Komossa
& Fink 1997a; for brief summaries of these papers see Sects. 1 and 5 of
Komossa & Fink 1997a). Recently, first BeppoSAX results have been
presented by Guainazzi et al. (1998a), who report the detection of a
strong drop in source flux which lasted the whole observing interval
of ~ 2 d.

20. 2000A&A...354..411K
Re:NGC 4051
NGC 4051. We analyzed all ROSAT PSPC observations of this well-known
Seyfert galaxy including previously unpublished ones. Variability by a
factor of ~ 30 in countrate is detected. The mean X-ray luminosity
varies less but still by a factor of ~ 7, whereas the properties of the
warm absorber (U, N_w_; averaged over individual pointings) change by
only a factor of ~ 2, indicating that the bulk of the warm absorber is
either of low density or out of photoionization equilibrium.

21. 1999ApJ...526L...9P
Re:NGC 4051
This Seyfert 1 galaxy was observed in the radio by Ulvestad & Wilson
(1984) and has a radio jet along P.A. = 81^deg^. From kinematical data,
Lizst & Dickey (1995) found i = 39^deg^ and {delta} = 51^deg^. Fitting
the Fe K{alpha} ASCA spectrum, Nandra et al. (1997) found
i_disk_ = 33^+5^_-13_ degrees. Using the rotation curve of the galaxy
and assuming that the spiral arms are trailing, we find that the
southwest side of the galaxy is the nearer side, so that the jet is
projected against the side of the galaxy farthest from us. Using these
values and equation (3), we find that {beta} ~ 23^deg^. Note again that
the errors in the determination of i_disk_ are large so that the results
should be taken with caution.

22. 1998ApJS..114...73G
Re:NGC 4051
Section A7. NGC 4051
This Seyfert 1.5 galaxy was first detected in X-rays by Einstein (Marshall et
al. 1983) and has been seen to exhibit rapid variability on timescales as
short as few x 10^2^ s (see, e.g., Lawrence et al. 1987). Indeed, in Paper I
we showed NGC 4051 to be the source to exhibit the most pronounced
variability of any of the sources considered. Absorption due to ionized gas
in this object was first suggested by ROSAT PSPC observations (Pounds et al.
1994). In our analysis of the data from the ASCA observation performed in
1993 April, we find no model in Section 5 that satisfies our formal criteria
for acceptability. A satisfactory fit is found, however, if a strong (F~4)
Compton-reflection component is included in the model (Section 6.4.1).
.
However, such a curvature in the observed spectrum may be due in part to the
spectral variability observed during the observation (Paper I). Nevertheless,
we do find a significant improvement in the fits for models including ionized
gas, with U_X_ ~ 0.7, N_H, z_ ~ 2-10 x 10^22^ cm^-2^, and {GAMMA} ~ 2.3 for
all models B(i)-C(ii), and U_X_ ~ 0.4, N_H, z_ ~ 10^22^ cm^-2^, and {GAMMA} ~
2.4 for the model including Compton reflection (Table 10). Mihara et al.
(1994) and R97 have both performed independent analyses of this ASCA data
set. Both find the addition of two edges to a single-power-law model
significantly improved the goodness of fit over the 0.6-1.0 keV band, which
confirms the results from the ROSAT PSPC and from a later ASCA observation
carried out in 1994 July (Guainazzi et al. 1996). R97 fixed the edge energies
to those appropriate for O VII and O VIII and found {tau}_O7_ ~ {tau}_O8_ ~
0.2.

23. 1998ApJS..114...73G
Re:NGC 4051
Photoionization models were also applied to these ASCA data by Mihara et al.
and R97, as well as to the earlier ROSAT PSPC data (Pounds et al. 1994;
McHardy et al. 1995) and data from the later ASCA observation (Guainazzi et
al. 1996). Unfortunately, detailed comparisons are difficult because of
differing assumptions regarding the form of the observed and photoionized
spectra. Mihara et al. find {xi} ~ 50 (but for an unspecified XUV continuum)
and N_H, z_ ~ 2 x 10^21^ cm^-2^ when the observed continuum is modeled by a
(relatively) flat power law ({GAMMA} ~ 1.9) plus a low-temperature blackbody
(kT ~ 0.1 keV and luminosity L_bb_ ~ 3 x 10^41^ ergs s^-1^). R97 find
U^R97^_X_ ~ 0.02, N_H, z_ ~ 10^21^ cm^-2^ and {GAMMA} ~ 1.9 but also find
evidence for a similar blackbody component. From the analysis of combined
ROSAT-Ginga data, Pounds et al. (1994) also prefer the inclusion of a
blackbody (kT ~ 0.2 keV and L_bb_ ~ 5 x 10^41^ ergs s^-1^) and power law
({GAMMA} ~ 2.1) finding N_H, z_ ~ 7 x 10^22^ cm^-2^ and U ~ 0.8 (but for an
un specified XUV continuum). From subsequent ROSAT data McHardy et al. (1995)
find U_X_ ~ 0.5 (given their continuum), N_H, z_ ~ 8 x 10^22^ cm^-2^ and
{GAMMA} ~ 2.2, with no requirement for a cool thermal component. Finally,
Guainazzi et al. find N_H_, z ~ 2 x 10^22^ cm^-2^, {GAMMA} ~ 2.1, and U_X_ ~
0.2 (given their continuum). These workers found evidence for additional
emission <~1 keV, which could be modeled by either a blackbody or a series of
emission lines. However, given the differential variability between the
depths of the O VII and O VIII edges seen on a timescale ~10^4^ s during the
1994 observation, Guainazzi et al. considered neither explanation to be
satisfactory. We find no strong requirement for a low-temperature blackbody
component in our analysis of NGC 4051 (with our models for having 1.0 <~
R_0.6_^bar^ <~ 1.2). For our model including Compton reflection, we find
L_bb_ <~ 3 x 10^41^ ergs s^-1^ for kT = 0.1 keV. Instead, our findings do
imply significant emission from the photoionized gas in NGC 4051 at energies
<~1 keV (with a luminosity of ~10^41^ ergs s^-1^ in the 0.1-1 keV band),
emission that was ascribed to the blackbody component by previous workers.
However, we do note that the derived intensity of this emission is up to a
factor of 3 times that expected given the intensity of the continuum during
the observations. It is currently unclear whether these results indicate
that the source was brighter in the past, that there is indeed an additional
component at the softest energies, or that the physical conditions with
NGC 4051 are much more complex. We consider it unlikely that significant
progress in decoupling the complex spectral variability exhibited by NGC 4051
<~ 1 keV will be made until high signal-to-noise ratio observations are
performed with high spectral and temporal resolution. Nevertheless, the
time-averaged results presented here are useful for comparison with those
from those sources that appear to exhibit less dramatic variability.
.
NP94 found evidence for absorption by ionized gas in Ginga observations, with
N_H, z_ ~ 6 x 10^22^ cm^-2^.

24. 1998ApJ...500..685P
Re:NGC 4051
5. NGC 4051.--NGC 4051 is a Seyfert type 1 galaxy hosted by an SABbc. Many H II
regions are seen along the spiral arms. NGC 4051 requires again three thermal
components to fit its mid- and far-IR SED. The central temperatures of these
three components are 18, 47, and 151 K, with widths of 3, 11, and 43 K,
respectively. The cold 47 K and warm 151 K components are in this case equally
important. As in NGC 3227 and NGC 3982 the cold component is likely related to
emission by dust heated by young OB stars in star-forming regions. The warm
component, which is also very intense in this galaxy, and responsible of the
strong continuum shorter of 30 {mu}m, is due to dust in the form of small grains
heated either directly by the nucleus or by very massive stars in circumnuclear
starbursts (Rodriguez Espinosa & Perez Garcia 1997, and references therein).

25. 1997MNRAS.286..513R
Re:NGC 4051
7.1.8 NGC 4051
The soft X-ray properties of this Seyfert 1 galaxy are complex. The
time-averaged soft ASCA PV spectrum (Mihara et al. 1994 and the present work)
can be explained as a combination of a primary power law, a blackbody soft
excess and the effects of ionized absorption. The present work completely
agrees with that of Mihara et al. (1994). The blackbody soft excess has a
best-fitting temperature kT=0.12+/-0.01 keV and a bolometric luminosity
L_B_=2.3x10^41^ erg s^-1^.
Complex spectral variability has been reported by Guainazzi et al. (1996)
during a later ASCA observation of NGC 4051. These authors find that, in a
two-edge parametrization, both the best-fitting edge depth and edge energies
increase when the source enters a low state. However, it is unclear how to
interpret these results: a complex interplay of a variable ionized absorber
with a variable soft excess could lead to misleading results when an
oversimplified spectral model is fitted. An unidentified spectral feature at
~0.9 keV may also affect conclusions about spectral variability. Observations
of higher spectral resolution with future missions (e.g. ASTRO-E and AXAF) will
be invaluable in understanding this complex source.

26. 1997ApJS..112..391H
Re:NGC 4051
NGC 4051.--With an absolute blue magnitude of only -15.6 (Veron 1979, assuming
H_0_=50 km s^-1^ Mpc^-1^), the nucleus of NGC 4051 can be considered the least
luminous classical type 1 Seyfert (Weedman 1976). As with other prominent
Seyfert 1 nuclei (e.g., NGC 3516; Fig. 6c), we removed the narrow-line
contribution to the complex with a model constructed from the [S II] lines
(Fig. 11c). The broad H{alpha} line has unusually small widths (FWHM~1000
km s^-1^, FWZI~5900 km s^-1^) compared with other objects of its class (e.g.,
NGC 4151, NGC 5548), and this object most likely belongs to the group of
narrow-lined Seyfert 1 nuclei (Osterbrock & Pogge 1985). Both H{beta} and
H{gamma} also have broad components.

27. 1997ApJS..110..299M
Re:NGC 4051
The spiral arms appear to emanate from a bar structure in the image. The
ellipse fits have the signature of a bar, although we do not trace the
full length of the bar. Unbarred in the RSA.

28. 1997ApJS..108..155G
Re:NGC 4051
This is one of the weakest S1 nuclei, hosted in an Sbc galaxy. The
circumnuclear emission is extended 8" to the northeast in H{alpha} and
[O III] (Fig. 11h). Radio continuum emission at 6 cm shows two sources
extended 1.5" in total and aligned in the east direction (Haniff, Wilson,
& Ward 1988). H II regions are detected along the spiral arms.

29. 1997A&A...319...33A
Re:NGC 4051
NGC 4051 A figure is not shown here but Table 1 indicates there is a strong
pair of sources well aligned across this Seyfert. The pair is probably false,
however, because the position of the C=30.7 source falls on a bright star,
E=9.2 mag. It is, of course, always possible that some faint extragalactic
objects could be masked by the bright star but the probability seems high that
the source of the X-rays is the star. The other member of the pair at C=17.0
has a good BSO candidate but it lies 88.5" off the X-ray position, too far to
be considered an identification.
There is one interesting source, very bright at C=72.4, about 16.7' NW of the
Seyfert. As the identification chart in the appendix shows, there is a group of
blue objects roughly surrounding a bluish, compact galaxy. Four of the five
BSO's are accurately aligned in a cross pattern across the central blue galaxy.
With so many candidates one has to consider the possibility that the red or
blue Schmidt plate might be miscalibrated in this region. If the colors are
accurate, however, this would be an extrordinarily interesting group to
investigate spectroscopically.

30. 1996ApJS..105...93E
Re:NGC 4051
4.7. NGC 4051
This nucleus of this famous Seyfert 1 galaxy has been the subject of many
intensive studies (e.g., de Robertis & Osterbrock 1984; Pogge 1989; Veilleux
1991; Hunt et al. 1992; Kunieda et al. 1992). Detailed optical emission-line
and continuum contour maps of the inner few arcseconds surrounding the nucleus
are available (Haniff, Wilson, & Ward 1988). Byrd, Sundelius, & Valtonen (1987)
suggest that the Seyfert activity may have been triggered tidally through
interactions with NGC 4013, which is separated from NGC 4051 by ~240 kpc.
Figure 1 demonstrates that the brightest giant H II regions trace the spiral
arms structure out to ~2' radius. Compact H II regions are discernible
individually closer to the nucleus, down to ~15" radius. Within this radius,
there is evidence for widespread, diffuse H{alpha} emission rather than
distinct compact H{alpha} sources.

31. 1996ApJ...463..498S
Re:NGC 4051
A7. NGC 4051
The [O III] emission of this Seyfert 1 galaxy is unresolved from ground-based
observations (Haniff, Wilson, & Ward 1988; Pogge 1989). Ulvestad & Wilson
(1984a) obtained VLA radio maps that show that this galaxy has two components
separated by 0.4" along PA 90^deg^. Our image shows an unresolved nucleus and
some extended emission with a blob displaced by 0.5" (24 pc) from the nucleus
with PA 100^deg^. This structure is similar to the radio structure found by
Ulvestad & Wilson (1984a). The total extent of the emission is 1.2" (58 pc).

32. 1996A&A...309...81W
Re:NGC 4051
NGC4051
The X-ray spectrum of this Seyfert galaxy has been extensively discussed.
Recently, simultaneous observations by ROSAT and Ginga have been analyzed by
Pounds et al. (1994). They found at the complex X-ray spectrum is most likely
due to a warm absorber. We used publicly available pointed observations of
January 1991. A single power law with cold absorption cannot fit the high
signal-to-noise ratio data. A single power law with absorption by warm
material fits the data very well (Fig. 2c), though adding a soft blackbody
component also improves the X^2^ to an acceptable value. For a warm absorption
model, the derived value of N_{omega}_ is (3.76+/-1.45)x10^22^ cm^-2^. The
photoionization parameter U=N_ion_/4{pi}R^2^n_e_c, (n_e_ is the hydrogen
density, c the speed of light, N_ion_ the number of ionizing photons, and R
the distance of the gas from the ionizing source) is approximately
17^+30^_-13_. This value is much larger than typically obtained (0.01-0.1) for
conventional BLR material (e.g. Ferland et al. 1992).

33. 1995MNRAS.276.1262K
Re:NGC 4051
NGC 4051: Type 1. Host galaxy: SB (CPG), Sb or SBc (UGC). Radio: the C-
array map shows a bright elongated source with extensions to the north-
east and south-west. The brightest part of the C-array map is resolved
into a point source with A-array, but most of the flux appears to come
from the extended structure. NGC 4051 is known to contain 0.4-arcsec
double from the 5-GHz measurements of Ulvestad & Wilson (1984b) and there
does appear to be a marginal detection of the weaker, eastern component
in the current A-array map, but at a level which makes an accurate
determination of its flux impossible.

34. 1995ApJS...98..477H
Re:NGC 4051
NGC 4051 is the lowest luminosity ``classical'' Seyfert 1 galaxy (Veron
1979). He II {lambda}4686 and [Fe X] {lambda}6374 are particularly
noticeable in Figure 47. Relative to most other Seyfert 1 galaxies
(e.g., NGC 5548 in Fig. 85), the permitted lines of NGC 4051 are
conspicuously narrow.

35. 1994CAG1..B...0000S
Re:NGC 4051
Sbc(r)II
PH-8056-S
Feb 4/5, 1981
103aO
12 min
NGC 4051 is one of the original six
emission-line galaxies used by Seyfert (1943) in
his discussion of Mount Wilson spectra and direct
plates of a class of galaxies known initially to
Humason, to Minkowski, and to Hubble to have
starlike (unresolved) nuclei and very broad
emission lines in their spectra.
The beginning of the modern work on
Seyfert galaxies and related objects, now called
active galactic nuclei (AGN), was made in a seminal
paper by Woltjer (1959). Seyfert galaxies
and quasars are the most prominent examples of
this class. Quasars are maxi-Seyferts.
Short-exposure plates of NGC 4051 and
direct visual inspection at a large telescope show
an intense starlike (unresolved) nucleus which is
a mini-quasar at the center of the galaxy.
The outer spiral structure is nearly of the
grand design type, having only several major
arms rather than a series of fragments as in the
MAS type.
The largest of the many HII regions in the
several arms resolve (core plus halo) at about the
4" level. The redshift of NGC 4051 is v_o = 746 km/s.

36. 1993ApJ...419..553B
Re:NGC 4051
NGC 4051 (UGC 07030)
NGC 4051 is a Seyfert 1 Sb/SBc galaxy with an inclination of
i~40^deg^ (e.g., Adams 1977). Smith et al. (1983) detected extended far-IR
emission with the Kuiper Airborne Observatory and suggested that NGC 4051
possesses a modest outgoing starburst. Ulvestad & Wilson (1984a)
presented 6 and 20 cm VLA images showing that on the subkiloparsec scale
the source is comprised of two main components separated by 0.4" (~16 Pc)
along an east west direction and diffuse emission extending mainly ~2"
(~80 Pc) to the southwest. Our WSRT 6 cm image (Fig. 8, 3.5" x 5.7"
resolution) shows that on an intermediate scale the source appears
roughly banana shaped with its major axis oriented along P.A. 32^deg^
(the minor axis of the host galaxy), and a total extent of roughly 15"
(~600 Pc). Moving down in resolution, the appearance of the source
continues to change. Figure 8b shows the source as imaged by the VLA in
the D-array at 6 cm (21" x 14" at P.A. 90^deg^ resolution from Baum et
al. 1993a). Now diffuse radio emission associated with the spiral arms of
the galaxy becomes apparent (compare with the reproduction of the
digitized POSS image at the same scale in Fig. 8c). A hint of this
structure can also be seen in the image presented by Hummel et al.
(1985). Finally, at 20 cm in the VLA D-array (Fig. 8d, 72" x 46" at P.A.
80^deg^ resolution from Baum et al. 1993a; see also Condon 1987), large-
scale radio emission associated with the entire galaxy disk is detected.
Thus in NGC 4051 we clearly detect three radio components-nuclear,
extranuclear, and disk radio emission.

37. 1976RC2...C...0000d
Re:NGC 4051
Type 1 Seyfert nucleus. B_N = 14.60, B_T(excluding nucleus) = 10.99.
Description and Classification:
P.A.S.P., 77, 287, 1965.
P.A.S.P., 79, 152, 1967.
"Nuclei of Galaxies", p.27, 1971.
Diameter of faint nucleus:
A.J., 73, S175, 1968.
Photograph:
Publ. Dept. A. Univ. Texas, II, 2, No. 7, 1968.
"Nuclei of Galaxies", p.27, 1971.
Sov. A.J., 17, 643, 1971.
Photometry:
A.J., 73, 858, 1968.
Publ.Dept.A.Univ.Texas, II, 2, No. 7, 1968.
Photometry (12 Color):
Ap. J., 145, 36, 1966.
Photometry (UBV):
Ap. J. (Letters), 150, L177, 1967.
A.J., 73, 866, 1968.
Sov. A.J., 17, 169, 1973.
M.N.R.A.S., 167, 1P, 1974.
M.N.R.A.S., 169, 357, 1974.
Atti. Conv. Sci. Osserv. Cima Ekar, Padova-Asiago, 101, 1973 =
Cont. Asiago, No. 300b.
Isophotometry:
Sov. A.J., 17, 643, 1974.
Photometry (I.R. 1-10 microns):
A.J., 73, 866, 870, 1968.
Ap. J. (Letters), 176, L95, 1972.
M.N.R.A.S., 169, 357, 1974.
"Nuclei of Galaxies", p.195, 1971.
Spectrum:
Ap. J., 192, 581, 1974.
Spectrophotometry:
Ap. J. (Letters), 154, L53, 1968.
Ap. J., 162, 743, 1970.
Ap. J., 164, 1, 1971.
Sov. A.J., 11, 767, 1967.
Ast. Tsirk. No. 467, 1968.
IAU Symp. No.29, 83, 1968.
C.R. Acad. Sc., B, 270, 238, 1970.
Astr. Ap., 27, 433, 1973.
"Nuclei of Galaxies", 151, 1971.
Polarization:
Ast. Tsirk. No. 454, 1967.
Astrofizika, 4, 409, 1968.
Astrofizika, 7, 417, 1971.
HI 21cm:
Astr. Ap., 10, 198, 1971.
IAU Symp. No.44, p.267, 1972.
Radio Observations:
A.J., 73, 876, 1968.
Astr. Ap., 15, 110, 1971.

38. 1973UGC...C...0000N
Re:UGC 07030
SAB(rs)bc (de Vaucouleurs), Sc- (Holmberg)

39. 1964RC1...C...0000d
Re:NGC 4051
Very small, extremely bright nucleus or star. Pseudo (r): 1.8 arcmin x
0.8 arcmin. 2 main, partially resolved branching arms.
See also HA 105, 230, 1937.
Photograph:
Ap. J., 130, 26, 1959.
Spectrum: Broad emission lines.
Ap. J., 97, 28, 1943.
HII Regions:
Zeit. fur Ap., 50, 168, 1960.

40. 1918PLicO..13....9C
Re:NGC 4051
A fine, rather bright spiral 4' x 2' in p.a. 122^deg^. Very bright stellar
nucleus. There are numerous almost stellar condensations. It is a two-branched
spiral, and each branch is bifid. 15 s.n.


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